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+<H1>15. ADMINISTERING POSTGRES</H1>
+<HR>
+ In this section, we will discuss aspects of POSTGRES
+ that are of interest to those who make extensive use of
+ POSTGRES, or who are the site administrator for a group
+ of POSTGRES users.
+
+<H2>15.1. Frequent Tasks</H2>
+ Here we will briefly discuss some procedures that you
+ should be familiar with in managing any POSTGRES
+ installation.
+
+<H3>15.1.1. Starting the Postmaster</H3>
+ If you did not install POSTGRES exactly as described in
+ the installation instructions, you may have to perform
+ some additional steps before starting the postmaster
+ process.
+ <UL>
+ <LI>Even if you were not the person who installed POSTGRES,
+ you should understand the installation
+ instructions. The installation instructions explain
+ some important issues with respect to where POSTGRES
+ places some important files, proper settings for
+ environment variables, etc. that may vary from one
+ version of POSTGRES to another.<p>
+ <LI>You must start the postmaster process with the userid
+ that owns the installed database files. In most
+ cases, if you have followed the installation
+ instructions, this will be the user "<B>postgres</B>". If
+ you do not start the postmaster with the right userid,
+ the backend servers that are started by the
+ postmaster will not be able to read the data.<p>
+ <LI>Make sure that <CODE>/usr/local/postgres95/bin</CODE> is in your
+ shell command path, because the postmaster will use
+ your <B>PATH</B> to locate POSTGRES commands.<p>
+ <LI>Remember to set the environment variable <B>PGDATA</B> to
+ the directory where the POSTGRES databases are
+ installed. (This variable is more fully explained
+ in the POSTGRES installation instructions.)<p>
+ <LI>If you do start the postmaster using non-standard
+ options, such as a different TCP port number, remember
+ to tell all users so that they can set their
+ <B>PGPORT</B> environment variable correctly.<p>
+ </UL>
+
+<H3>15.1.2. Shutting Down the Postmaster</H3>
+ If you need to halt the postmaster process, you can use
+ the <B>UNIX</B> <B>kill(1)</B> command. Some people habitually use
+ the <B>-9</B> or <B>-KILL</B> option; this should never be necessary
+ and we do not recommend that you do this, as the postmaster
+ will be unable to free its various shared
+ resources, its child processes will be unable to exit
+ gracefully, etc.
+
+<H3>15.1.3. Adding and Removing Users</H3>
+ The createuser and destroyuser commands enable and disable
+ access to POSTGRES by specific users on the host
+ system.
+
+<H3>15.1.4. Periodic Upkeep</H3>
+ The vacuum command should be run on each database periodically.
+ This command processes deleted instances<A HREF="#9"><font size=-1>[9]</font></A>
+ and, more importantly, updates the system statistics
+ concerning the size of each class. If these statistics
+ are permitted to become out-of-date and inaccurate, the
+ POSTGRES query optimizer may make extremely poor decisions
+ with respect to query evaluation strategies.
+ Therefore, we recommend running vacuum every night or
+ so (perhaps in a script that is executed by the <B>UNIX</B>
+ <B>cron(1)</B> or <B>at(1)</B> commands).
+ Do frequent backups. That is, you should either back
+ up your database directories using the POSTGRES copy
+ command and/or the <B>UNIX</B> <B>dump(1)</B> or <B>tar(1)</B> commands.
+ You may think, "Why am I backing up my database? What
+ about crash recovery?" One side effect of the POSTGRES
+ "no overwrite" storage manager is that it is also a "no
+ log" storage manager. That is, the database log stores
+ only abort/commit data, and this is not enough information
+ to recover the database if the storage medium
+ (disk) or the database files are corrupted! In other
+ words, if a disk block goes bad or POSTGRES happens to
+ corrupt a database file, you cannot recover that file.
+ This can be disastrous if the file is one of the shared
+ catalogs, such as pg_database.
+
+<H3>15.1.5. Tuning</H3>
+ Once your users start to load a significant amount of
+ data, you will typically run into performance problems.
+ POSTGRES is not the fastest DBMS in the world, but many
+ of the worst problems encountered by users are due to
+ their lack of experience with any DBMS. Some general
+ tips include:
+ <OL>
+ <LI> Define indices over attributes that are commonly
+ used for qualifications. For example, if you
+ often execute queries of the form
+
+<pre> SELECT * from EMP where salary < 5000
+</pre>
+ then a B-tree index on the salary attribute will
+ probably be useful. If scans involving equality
+ are more common, as in
+
+<pre> SELECT * from EMP where salary = 5000
+</pre>
+ then you should consider defining a hash index
+ on salary. You can define both, though it will
+ use more disk space and may slow down updates a
+ bit. Scans using indices are much faster than
+ sequential scans of the entire class.<p>
+ <LI> Run the vacuum command a lot. This command
+ updates the statistics that the query optimizer
+ uses to make intelligent decisions; if the
+ statistics are inaccurate, the system will make
+ inordinately stupid decisions with respect to
+ the way it joins and scans classes.<p>
+ <LI> When specifying query qualfications (i.e., the
+ where part of the query), try to ensure that a
+ clause involving a constant can be turned into
+ one of the form range_variable operator constant, e.g.,
+
+<pre> EMP.salary = 5000
+</pre>
+ The POSTGRES query optimizer will only use an
+ index with a constant qualification of this
+ form. It doesn't hurt to write the clause as
+
+<pre> 5000 = EMP.salary
+</pre>
+ if the operator (in this case, =) has a commutator
+ operator defined so that POSTGRES can
+ rewrite the query into the desired form. However,
+ if such an operator does not exist, POSTGRES
+ will never consider the use of an index.<p>
+ <LI> When joining several classes together in one
+ query, try to write the join clauses in a
+ "chained" form, e.g.,
+
+<pre> where A.a = B.b and B.b = C.c and ...
+</pre>
+ Notice that relatively few clauses refer to a
+ given class and attribute; the clauses form a
+ linear sequence connecting the attributes, like
+ links in a chain. This is preferable to a query
+ written in a "star" form, such as
+
+<pre> where A.a = B.b and A.a = C.c and ...
+</pre>
+ Here, many clauses refer to the same class and
+ attribute (in this case, A.a). When presented
+ with a query of this form, the POSTGRES query
+ optimizer will tend to consider far more choices
+ than it should and may run out of memory.<p>
+ <LI> If you are really desperate to see what query
+ plans look like, you can run the postmaster with
+ the -d option and then run monitor with the -t
+ option. The format in which query plans will be
+ printed is hard to read but you should be able
+ to tell whether any index scans are being performed.<br>
+</OL>
+
+<H2>15.2. Infrequent Tasks</H2>
+
+ At some time or another, every POSTGRES site
+ administrator has to perform all of the following actions.
+
+15.2.1. Cleaning Up After Crashes
+ The <B>postgres</B> server and the <B>postmaster</B> run as two
+ different processes. They may crash separately or
+ together. The housekeeping procedures required to fix
+ one kind of crash are different from those required to
+ fix the other.
+ The message you will usually see when the backend
+ server crashes is:
+
+<pre> FATAL: no response from backend: detected in ...
+</pre>
+ This generally means one of two things: there is a bug
+ in the POSTGRES server, or there is a bug in some user
+ code that has been dynamically loaded into POSTGRES.
+ You should be able to restart your application and
+ resume processing, but there are some considerations:
+ <OL>
+ <LI> POSTGRES usually dumps a core file (a snapshot
+ of process memory used for debugging) in the
+ database directory
+<pre> /usr/local/postgres95/data/base/<database>/core
+</pre>
+ on the server machine. If you don't want to try
+ to debug the problem or produce a stack trace to
+ report the bug to someone else, you can delete
+ this file (which is probably around 10MB).<p>
+ <LI> When one backend crashes in an uncontrolled way
+ (i.e., without calling its built-in cleanup
+ routines), the postmaster will detect this situation,
+ kill all running servers and reinitialize
+ the state shared among all backends (e.g., the
+ shared buffer pool and locks). If your server
+ crashed, you will get the "no response" message
+ shown above. If your server was killed because
+ someone else's server crashed, you will see the
+ following message:
+
+<pre> I have been signalled by the postmaster.
+ Some backend process has died unexpectedly and possibly
+ corrupted shared memory. The current transaction was
+ aborted, and I am going to exit. Please resend the
+ last query. -- The postgres backend
+</pre><br>
+ <LI> Sometimes shared state is not completely cleaned
+ up. Frontend applications may see errors of the
+ form:
+
+<pre> WARN: cannot write block 34 of myclass [mydb] blind
+</pre>
+ In this case, you should kill the postmaster and
+ restart it.<p>
+ <LI> When the system crashes while updating the system
+ catalogs (e.g., when you are creating a
+ class, defining an index, retrieving into a
+ class, etc.) the B-tree indices defined on the
+ catalogs are sometimes corrupted. The general
+ (and non-unique) symptom is that all queries
+ stop working. If you have tried all of the
+ above steps and nothing else seems to work, try
+ using the reindexdb command. If reindexdb succeeds
+ but things still don't work, you have
+ another problem; if it fails, the system catalogs
+ themselves were almost certainly corrupted
+ and you will have to go back to your backups.<p>
+ </OL>
+ The postmaster does not usually crash (it doesn't do
+ very much except start servers) but it does happen on
+ occasion. In addition, there are a few cases where it
+ encounters problems during the reinitialization of
+ shared resources. Specifically, there are race conditions
+ where the operating system lets the postmaster
+ free shared resources but then will not permit it to
+ reallocate the same amount of shared resources (even
+ when there is no contention).
+ You will typically have to run the ipcclean command if
+ system errors cause the postmaster to crash. If this
+ happens, you may find (using the UNIX ipcs(1) command)
+ that the "<B>postgres</B>" user has shared memory and/or
+ semaphores allocated even though no postmaster process
+ is running. In this case, you should run ipcclean as
+ the "<B>postgres</B>" user in order to deallocate these
+ resources. Be warned that all such resources owned by
+ the "<B>postgres</B>" user will be deallocated. If you have
+ multiple postmaster processes running on the same
+ machine, you should kill all of them before running
+ ipcclean (otherwise, they will crash on their own when
+ their shared resources are suddenly deallocated).
+
+<H3>15.2.2. Moving Database Directories</H3>
+ By default, all POSTGRES databases are stored in
+ separate subdirectories under
+ <CODE>/usr/local/postgres95/data/base</CODE>.<A HREF="#10"><font size=-1>[10]</font></A> At some point, you
+ may find that you wish to move one or more databases to
+ another location (e.g., to a filesystem with more free
+ space).
+ If you wish to move all of your databases to the new
+ location, you can simply:
+ <UL>
+ <LI>Kill the postmaster.<p>
+ <LI>Copy the entire data directory to the new location
+ (making sure that the new files are owned by user
+ "<B>postgres</B>").
+
+<pre> % cp -rp /usr/local/postgres95/data /new/place/data
+</pre><p>
+ <LI>Reset your PGDATA environment variable (as described
+ earlier in this manual and in the installation
+ instructions).
+
+<pre> # using csh or tcsh...
+ % setenv PGDATA /new/place/data
+
+ # using sh, ksh or bash...
+ % PGDATA=/new/place/data; export PGDATA
+
+</pre><p>
+ <LI>Restart the postmaster.
+
+<pre> % postmaster &
+</pre><p>
+ <LI>After you run some queries and are sure that the
+ newly-moved database works, you can remove the old
+ data directory.
+<pre> % rm -rf /usr/local/postgres95/data
+</pre><p>
+</UL>
+ To install a single database in an alternate directory
+ while leaving all other databases in place, do the following:
+<UL>
+ <LI>Create the database (if it doesn't already exist)
+ using the createdb command. In the following steps
+ we will assume the database is named foo.<p>
+ <LI>Kill the postmaster.<p>
+ <LI>Copy the directory
+ <CODE>/usr/local/postgres95/data/base/foo</CODE> and its contents
+ to its ultimate destination. It should still be
+ owned by the "<B>postgres</B>" user.
+
+<pre> % cp -rp /usr/local/postgres95/data/base/foo /new/place/foo
+</pre>
+ <LI>Remove the directory
+ <CODE>/usr/local/postgres95/data/base/foo</CODE>:
+
+<pre> % rm -rf /usr/local/postgres95/data/base/foo
+</pre>
+ <LI>Make a symbolic link from
+ <CODE>/usr/local/postgres95/data/base</CODE> to the new directory:
+
+<pre> % ln -s /new/place/foo /usr/local/postgres95/data/base/foo
+</pre>
+ <LI>Restart the postmaster.
+</UL>
+<p>
+<H3>15.2.3. Updating Databases</H3>
+ POSTGRES is a research system. In general, POSTGRES
+ may not retain the same binary format for the storage
+ of databases from release to release. Therefore, when
+ you update your POSTGRES software, you will probably
+ have to modify your databases as well. This is a common
+ occurrence with commercial database systems as
+ well; unfortunately, unlike commercial systems, POSTGRES
+ does not come with user-friendly utilities to make
+ your life easier when these updates occur.
+ In general, you must do the following to update your
+ databases to a new software release:
+ <UL>
+ <LI>Extensions (such as user-defined types, functions,
+ aggregates, etc.) must be reloaded by re-executing
+ the <B>SQL CREATE</B> commands. See Appendix A for more
+ details.
+ <LI>Data must be dumped from the old classes into ASCII
+ files (using the <B>COPY</B> command), the new classes created
+ in the new database (using the <B>CREATE TABLE</B>
+ command), and the data reloaded from the ASCII files.
+ <LI>Rules and views must also be reloaded by
+ reexecuting the various CREATE commands.
+ </UL>
+ You should give any new release a "trial period"; in
+ particular, do not delete the old database until you
+ are satisfied that there are no compatibility problems
+ with the new software. For example, you do not want to
+ discover that a bug in a type's "input" (conversion
+ from ASCII) and "output" (conversion to ASCII) routines
+ prevents you from reloading your data after you have
+ destroyed your old databases! (This should be standard
+ procedure when updating any software package, but some
+ people try to economize on disk space without applying
+ enough foresight.)
+
+<H2>15.3. Database Security</H2>
+
+ Most sites that use POSTGRES are educational or
+ research institutions and do not pay much attention to
+ security in their POSTGRES installations. If desired,
+ one can install POSTGRES with additional security
+ features. Naturally, such features come with additional
+ administrative overhead that must be dealt with.
+
+<H3>15.3.1. Kerberos</H3>
+ POSTGRES can be configured to use the <B>MIT</B> <B>Kerberos</B> network
+ authentication system. This prevents outside
+ users from connecting to your databases over the network
+ without the correct authentication information.
+<p>
+<H2>15.4. Querying the System Catalogs</H2>
+ As an administrator (or sometimes as a plain user), you
+ want to find out what extensions have been added to a
+ given database. The queries listed below are "canned"
+ queries that you can run on any database to get simple
+ answers. Before executing any of the queries below, be
+ sure to execute the POSTGRES <B>vacuum</B> command. (The
+ queries will run much more quickly that way.) Also,
+ note that these queries are also listed in
+<pre> /usr/local/postgres95/tutorial/syscat.sql
+</pre>
+ so use cut-and-paste (or the <B>\i</B> command) instead of
+ doing a lot of typing.
+ This query prints the names of all database adminstrators
+ and the name of their database(s).
+<pre> SELECT usename, datname
+ FROM pg_user, pg_database
+ WHERE usesysid = int2in(int4out(datdba))
+ ORDER BY usename, datname;
+</pre>
+ This query lists all user-defined classes in the
+ database.
+<pre> SELECT relname
+ FROM pg_class
+ WHERE relkind = 'r' -- not indices
+ and relname !~ '^pg_' -- not catalogs
+ and relname !~ '^Inv' -- not large objects
+ ORDER BY relname;
+</pre>
+ This query lists all simple indices (i.e., those that
+ are not defined over a function of several attributes).
+<pre> SELECT bc.relname AS class_name,
+ ic.relname AS index_name,
+ a.attname
+ FROM pg_class bc, -- base class
+ pg_class ic, -- index class
+ pg_index i,
+ pg_attribute a -- att in base
+ WHERE i.indrelid = bc.oid
+ and i.indexrelid = ic.oid
+ and i.indkey[0] = a.attnum
+ and a.attrelid = bc.oid
+ and i.indproc = '0'::oid -- no functional indices
+ ORDER BY class_name, index_name, attname;
+</pre>
+ This query prints a report of the user-defined
+ attributes and their types for all user-defined classes
+ in the database.
+<pre> SELECT c.relname, a.attname, t.typname
+ FROM pg_class c, pg_attribute a, pg_type t
+ WHERE c.relkind = 'r' -- no indices
+ and c.relname !~ '^pg_' -- no catalogs
+ and c.relname !~ '^Inv' -- no large objects
+ and a.attnum > 0 -- no system att's
+ and a.attrelid = c.oid
+ and a.atttypid = t.oid
+ ORDER BY relname, attname;
+</pre>
+ This query lists all user-defined base types (not
+ including array types).
+<pre> SELECT u.usename, t.typname
+ FROM pg_type t, pg_user u
+ WHERE u.usesysid = int2in(int4out(t.typowner))
+ and t.typrelid = '0'::oid -- no complex types
+ and t.typelem = '0'::oid -- no arrays
+ and u.usename <> 'postgres'
+ ORDER BY usename, typname;
+</pre>
+ This query lists all left-unary (post-fix) operators.
+<pre> SELECT o.oprname AS left_unary,
+ right.typname AS operand,
+ result.typname AS return_type
+ FROM pg_operator o, pg_type right, pg_type result
+ WHERE o.oprkind = 'l' -- left unary
+ and o.oprright = right.oid
+ and o.oprresult = result.oid
+ ORDER BY operand;
+</pre>
+ This query lists all right-unary (pre-fix) operators.
+<pre> SELECT o.oprname AS right_unary,
+ left.typname AS operand,
+ result.typname AS return_type
+ FROM pg_operator o, pg_type left, pg_type result
+ WHERE o.oprkind = 'r' -- right unary
+ and o.oprleft = left.oid
+ and o.oprresult = result.oid
+ ORDER BY operand;
+</pre>
+ This query lists all binary operators.
+<pre> SELECT o.oprname AS binary_op,
+ left.typname AS left_opr,
+ right.typname AS right_opr,
+ result.typname AS return_type
+ FROM pg_operator o, pg_type left, pg_type right, pg_type result
+ WHERE o.oprkind = 'b' -- binary
+ and o.oprleft = left.oid
+ and o.oprright = right.oid
+ and o.oprresult = result.oid
+ ORDER BY left_opr, right_opr;
+</pre>
+ This query returns the name, number of arguments
+ (parameters) and return type of all user-defined C
+ functions. The same query can be used to find all
+ built-in C functions if you change the "<B>C</B>" to "<B>internal</B>",
+ or all <B>SQL</B> functions if you change the "<B>C</B>" to
+ "<B>sql</B>".
+<pre> SELECT p.proname, p.pronargs, t.typname
+ FROM pg_proc p, pg_language l, pg_type t
+ WHERE p.prolang = l.oid
+ and p.prorettype = t.oid
+ and l.lanname = 'c'
+ ORDER BY proname;
+</pre>
+ This query lists all of the aggregate functions that
+ have been installed and the types to which they can be
+ applied. count is not included because it can take any
+ type as its argument.
+<pre> SELECT a.aggname, t.typname
+ FROM pg_aggregate a, pg_type t
+ WHERE a.aggbasetype = t.oid
+ ORDER BY aggname, typname;
+</pre>
+ This query lists all of the operator classes that can
+ be used with each access method as well as the operators
+ that can be used with the respective operator
+ classes.
+<pre> SELECT am.amname, opc.opcname, opr.oprname
+ FROM pg_am am, pg_amop amop, pg_opclass opc, pg_operator opr
+ WHERE amop.amopid = am.oid
+ and amop.amopclaid = opc.oid
+ and amop.amopopr = opr.oid
+ ORDER BY amname, opcname, oprname;
+</pre>
+<p>
+
+<HR>
+<A NAME="9"><B>9.</B></A>
+This may mean different things depending on the archive
+mode with which each class has been created. However, the
+current implementation of the vacuum command does not perform any compaction or clustering of data. Therefore, the
+UNIX files which store each POSTGRES class never shrink and
+the space "reclaimed" by vacuum is never actually reused.
+
+<HR width=50 align=left>
+<A NAME="10"><B>10.</B></A>
+Data for certain classes may stored elsewhere if a
+non-standard storage manager was specified when they were
+created. Use of non-standard storage managers is an experimental feature that is not supported outside of Berkeley.
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
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+ <TITLE>The POSTGRES95 User Manual - ADVANCED POSTGRES SQL FEATURES</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
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+<HR>
+<H1>5. ADVANCED POSTGRES <B>SQL</B> FEATURES</H1>
+<HR>
+ Having covered the basics of using POSTGRES <B>SQL</B> to
+ access your data, we will now discuss those features of
+ POSTGRES that distinguish it from conventional data
+ managers. These features include inheritance, time
+ travel and non-atomic data values (array- and
+ set-valued attributes).
+ Examples in this section can also be found in
+ <CODE>advance.sql</CODE> in the tutorial directory. (Refer to the
+ introduction of the <A HREF="query.html">previous chapter</A> for how to use
+ it.)
+
+<H2><A NAME="inheritance">5.1. Inheritance</A></H2>
+ Let's create two classes. The capitals class contains
+ state capitals which are also cities. Naturally, the
+ capitals class should inherit from cities.
+
+<pre> CREATE TABLE cities (
+ name text,
+ population float,
+ altitude int -- (in ft)
+ );
+
+ CREATE TABLE capitals (
+ state char2
+ ) INHERITS (cities);
+</pre>
+ In this case, an instance of capitals <B>inherits</B> all
+ attributes (name, population, and altitude) from its
+ parent, cities. The type of the attribute name is
+ <B>text</B>, a built-in POSTGRES type for variable length
+ ASCII strings. The type of the attribute population is
+ <B>float4</B>, a built-in POSTGRES type for double precision
+ floating point numbres. State capitals have an extra
+ attribute, state, that shows their state. In POSTGRES,
+ a class can inherit from zero or more other classes,<A HREF="#4"><font size=-1>[4]</font></A>
+ and a query can reference either all instances of a
+ class or all instances of a class plus all of its
+ descendants. For example, the following query finds
+ all the cities that are situated at an attitude of 500
+ 'ft or higher:
+
+<pre> SELECT name, altitude
+ FROM cities
+ WHERE altitude > 500;
+
+
+ +----------+----------+
+ |name | altitude |
+ +----------+----------+
+ |Las Vegas | 2174 |
+ +----------+----------+
+ |Mariposa | 1953 |
+ +----------+----------+
+</pre>
+ On the other hand, to find the names of all cities,
+ including state capitals, that are located at an altitude
+ over 500 'ft, the query is:
+
+<pre> SELECT c.name, c.altitude
+ FROM cities* c
+ WHERE c.altitude > 500;
+</pre>
+ which returns:
+
+<pre> +----------+----------+
+ |name | altitude |
+ +----------+----------+
+ |Las Vegas | 2174 |
+ +----------+----------+
+ |Mariposa | 1953 |
+ +----------+----------+
+ |Madison | 845 |
+ +----------+----------+
+</pre>
+ Here the * after cities indicates that the query should
+ be run over cities and all classes below cities in the
+ inheritance hierarchy. Many of the commands that we
+ have already discussed -- select, update and delete --
+ support this * notation, as do others, like alter command.
+
+<H2><A NAME="time-travel">5.2. Time Travel</A></H2>
+ POSTGRES supports the notion of time travel. This feature
+ allows a user to run historical queries. For
+ example, to find the current population of Mariposa
+ city, one would query:
+
+<pre> SELECT * FROM cities WHERE name = 'Mariposa';
+
+ +---------+------------+----------+
+ |name | population | altitude |
+ +---------+------------+----------+
+ |Mariposa | 1320 | 1953 |
+ +---------+------------+----------+
+</pre>
+ POSTGRES will automatically find the version of Mariposa's
+ record valid at the current time.
+ One can also give a time range. For example to see the
+ past and present populations of Mariposa, one would
+ query:
+
+<pre> SELECT name, population
+ FROM cities['epoch', 'now']
+ WHERE name = 'Mariposa';
+</pre>
+ where "epoch" indicates the beginning of the system
+ clock.<A HREF="#5"><font size=-1>[5]</font></A> If you have executed all of the examples so
+ far, then the above query returns:
+
+<pre> +---------+------------+
+ |name | population |
+ +---------+------------+
+ |Mariposa | 1200 |
+ +---------+------------+
+ |Mariposa | 1320 |
+ +---------+------------+
+</pre>
+ The default beginning of a time range is the earliest
+ time representable by the system and the default end is
+ the current time; thus, the above time range can be
+ abbreviated as ``[,].''
+
+<H2><A NAME="non-atomic-values">5.3. Non-Atomic Values</A></H2>
+ One of the tenets of the relational model is that the
+ attributes of a relation are atomic. POSTGRES does not
+ have this restriction; attributes can themselves contain
+ sub-values that can be accessed from the query
+ language. For example, you can create attributes that
+ are arrays of base types.
+
+<H3><A NAME="arrays">5.3.1. Arrays</A></H3>
+ POSTGRES allows attributes of an instance to be defined
+ as fixed-length or variable-length multi-dimensional
+ arrays. Arrays of any base type or user-defined type
+ can be created. To illustrate their use, we first create a
+ class with arrays of base types.
+
+<pre> * CREATE TABLE SAL_EMP (
+ name text,
+ pay_by_quarter int4[],
+ schedule char16[][]
+ );
+</pre>
+ The above query will create a class named SAL_EMP with
+ a <B>text</B> string (name), a one-dimensional array of <B>int4</B>
+ (pay_by_quarter), which represents the employee's
+ salary by quarter and a two-dimensional array of <B>char16</B>
+ (schedule), which represents the employee's weekly
+ schedule. Now we do some <B>INSERTS</B>s; note that when
+ appending to an array, we enclose the values within
+ braces and separate them by commas. If you know <B>C</B>,
+ this is not unlike the syntax for initializing structures.
+
+<pre> INSERT INTO SAL_EMP
+ VALUES ('Bill',
+ '{10000, 10000, 10000, 10000}',
+ '{{"meeting", "lunch"}, {}}');
+
+ INSERT INTO SAL_EMP
+ VALUES ('Carol',
+ '{20000, 25000, 25000, 25000}',
+ '{{"talk", "consult"}, {"meeting"}}');
+</pre>
+ By default, POSTGRES uses the "one-based" numbering
+ convention for arrays -- that is, an array of n elements starts with array[1] and ends with array[n].
+ Now, we can run some queries on SAL_EMP. First, we
+ show how to access a single element of an array at a
+ time. This query retrieves the names of the employees
+ whose pay changed in the second quarter:
+
+<pre> * SELECT name
+ FROM SAL_EMP
+ WHERE SAL_EMP.pay_by_quarter[1] <>
+ SAL_EMP.pay_by_quarter[2];
+
+ +------+
+ |name |
+ +------+
+ |Carol |
+ +------+
+</pre>
+ This query retrieves the third quarter pay of all
+ employees:
+
+<pre> * SELECT SAL_EMP.pay_by_quarter[3] FROM SAL_EMP;
+
+
+ +---------------+
+ |pay_by_quarter |
+ +---------------+
+ |10000 |
+ +---------------+
+ |25000 |
+ +---------------+
+</pre>
+ We can also access arbitrary slices of an array, or
+ subarrays. This query retrieves the first item on
+ Bill's schedule for the first two days of the week.
+
+<pre> * SELECT SAL_EMP.schedule[1:2][1:1]
+ FROM SAL_EMP
+ WHERE SAL_EMP.name = 'Bill';
+
+ +-------------------+
+ |schedule |
+ +-------------------+
+ |{{"meeting"},{""}} |
+ +-------------------+
+
+</pre>
+<p>
+<HR>
+<A NAME="4"><B>4.</B></A> i.e., the inheritance hierarchy is a directed acyclic
+graph.<br>
+<A NAME="5"><B>5.</B></A> On UNIX systems, this is always midnight, January 1,
+1970 GMT.<br>
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="query.html">[ Previous ]</A>
+<A HREF="extend.html">[ Next ]</A>
+</font>
+
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+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - Appendix A:</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="refs.html">[ Previous ]</A>
+[ Next ]
+</font>
+<HR>
+<H1>Appendix A: Linking Dynamically-Loaded Functions</H1>
+<HR>
+ After you have created and registered a user-defined
+ function, your work is essentially done. POSTGRES,
+ however, must load the object code (e.g., a .o file, or
+ a shared library) that implements your function. As
+ previously mentioned, POSTGRES loads your code at
+ runtime, as required. In order to allow your code to be
+ dynamically loaded, you may have to compile and
+ linkedit it in a special way. This section briefly
+ describes how to perform the compilation and
+ linkediting required before you can load your user-defined
+ functions into a running POSTGRES server. Note that
+ this process has changed as of Version 4.2.<A HREF="#11">11</A> You
+ should expect to read (and reread, and re-reread) the
+ manual pages for the C compiler, cc(1), and the link
+ editor, ld(1), if you have specific questions. In
+ addition, the regression test suites in the directory
+ /usr/local/postgres95/src/regress contain several
+ working examples of this process. If you copy what these
+ tests do, you should not have any problems.
+ The following terminology will be used below:
+ <DL>
+ <DT>Dynamic loading
+ <DD>is what POSTGRES does to an object file. The
+ object file is copied into the running POSTGRES
+ server and the functions and variables within the
+ file are made available to the functions within
+ the POSTGRES process. POSTGRES does this using
+ the dynamic loading mechanism provided by the
+ operating system.
+
+ <DT>Loading and link editing
+ <DD>is what you do to an object file in order to produce
+ another kind of object file (e.g., an executable
+ program or a shared library). You perform
+ this using the link editing program, ld(1).
+ </DL>
+<p>
+ The following general restrictions and notes also apply
+ to the discussion below.
+ <UL>
+ <LI>Paths given to the create function command must be
+ absolute paths (i.e., start with "/") that refer to
+ directories visible on the machine on which the
+ POSTGRES server is running.<A HREF="#12">12</A>
+ <LI>The POSTGRES user must be able to traverse the path
+ given to the create function command and be able to
+ read the object file. This is because the POSTGRES
+ server runs as the POSTGRES user, not as the user
+ who starts up the frontend process. (Making the
+ file or a higher-level directory unreadable and/or
+ unexecutable by the "postgres" user is an extremely
+ common mistake.)
+ <LI>Symbol names defined within object files must not
+ conflict with each other or with symbols defined in
+ POSTGRES.
+ <LI>The GNU C compiler usually does not provide the special
+ options that are required to use the operating
+ system's dynamic loader interface. In such cases,
+ the C compiler that comes with the operating system
+ must be used.
+ </UL>
+<p>
+<B>ULTRIX</B><br>
+ It is very easy to build dynamically-loaded object
+ files under ULTRIX. ULTRIX does not have any sharedlibrary
+ mechanism and hence does not place any restrictions on
+ the dynamic loader interface. On the other
+ hand, we had to (re)write a non-portable dynamic loader
+ ourselves and could not use true shared libraries.
+ Under ULTRIX, the only restriction is that you must
+ produce each object file with the option -G 0. (Notice
+ that that's the numeral ``0'' and not the letter
+ ``O''). For example,
+
+<pre> # simple ULTRIX example
+ % cc -G 0 -c foo.c
+</pre>
+ produces an object file called foo.o that can then be
+ dynamically loaded into POSTGRES. No additional loading or link-editing must be performed.
+<p>
+<B>DEC OSF/1</B><br>
+ Under DEC OSF/1, you can take any simple object file
+ and produce a shared object file by running the ld command over it with the correct options. The commands to
+ do this look like:
+
+<pre> # simple DEC OSF/1 example
+ % cc -c foo.c
+ % ld -shared -expect_unresolved '*' -o foo.so foo.o
+</pre>
+ The resulting shared object file can then be loaded
+ into POSTGRES. When specifying the object file name to
+ the create function command, one must give it the name
+ of the shared object file (ending in .so) rather than
+ the simple object file.<A HREF="#13">13</A> If the file you specify is
+ not a shared object, the backend will hang!
+<p>
+<B>SunOS 4.x, Solaris 2.x and HP-UX</B><br>
+ Under both SunOS 4.x, Solaris 2.x and HP-UX, the simple
+ object file must be created by compiling the source
+ file with special compiler flags and a shared library
+ must be produced.
+ The necessary steps with HP-UX are as follows. The +z
+ flag to the HP-UX C compiler produces so-called
+ "Position Independent Code" (PIC) and the +u flag
+ removes
+ some alignment restrictions that the PA-RISC architecture
+ normally enforces. The object file must be turned
+ into a shared library using the HP-UX link editor with
+ the -b option. This sounds complicated but is actually
+ very simple, since the commands to do it are just:
+<pre> # simple HP-UX example
+ % cc +z +u -c foo.c
+ % ld -b -o foo.sl foo.o
+</pre>
+
+ As with the .so files mentioned in the last subsection,
+ the create function command must be told which file is
+ the correct file to load (i.e., you must give it the
+ location of the shared library, or .sl file).
+ Under SunOS 4.x, the commands look like:
+
+<pre> # simple SunOS 4.x example
+ % cc -PIC -c foo.c
+ % ld -dc -dp -Bdynamic -o foo.so foo.o
+</pre>
+ and the equivalent lines under Solaris 2.x are:
+<pre> # simple Solaris 2.x example
+ % cc -K PIC -c foo.c
+ or
+ % gcc -fPIC -c foo.c
+ % ld -G -Bdynamic -o foo.so foo.o
+</pre>
+ When linking shared libraries, you may have to specify
+ some additional shared libraries (typically system
+ libraries, such as the C and math libraries) on your ld
+ command line.
+<HR>
+<A NAME="11"><B>11.</B></A> The old POSTGRES dynamic
+loading mechanism required
+in-depth knowledge in terms of executable format, placement
+and alignment of executable instructions within memory, etc.
+on the part of the person writing the dynamic loader. Such
+loaders tended to be slow and buggy. As of Version 4.2, the
+POSTGRES dynamic loading mechanism has been rewritten to use
+the dynamic loading mechanism provided by the operating
+system. This approach is generally faster, more reliable and
+more portable than our previous dynamic loading mechanism.
+The reason for this is that nearly all modern versions of
+UNIX use a dynamic loading mechanism to implement shared
+libraries and must therefore provide a fast and reliable
+mechanism. On the other hand, the object file must be
+postprocessed a bit before it can be loaded into POSTGRES. We
+hope that the large increase in speed and reliability will
+make up for the slight decrease in convenience.
+<hr width=50 align=left>
+<A NAME="12"><B>12.</B></A> Relative paths do in fact work,
+but are relative to
+the directory where the database resides (which is generally
+invisible to the frontend application). Obviously, it makes
+no sense to make the path relative to the directory in which
+the user started the frontend application, since the server
+could be running on a completely different machine!<br>
+<hr width=50 align=left>
+<A NAME="13"><B>13.</B></A> Actually, POSTGRES does not care
+what you name the
+file as long as it is a shared object file. If you prefer
+to name your shared object files with the extension .o, this
+is fine with POSTGRES so long as you make sure that the correct
+file name is given to the create function command. In
+other words, you must simply be consistent. However, from a
+pragmatic point of view, we discourage this practice because
+you will undoubtedly confuse yourself with regards to which
+files have been made into shared object files and which have
+not. For example, it's very hard to write Makefiles to do
+the link-editing automatically if both the object file and
+the shared object file end in .o!<br>
+
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="refs.html">[ Previous ]</A>
+[ Next ]
+</font>
+</BODY>
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+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - ARCHITECTURE</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="intro.html">[ Previous ]</A>
+<A HREF="start.html">[ Next ]</A>
+</font>
+<HR>
+<H1>2. POSTGRES ARCHITECTURE CONCEPTS</H1>
+<HR>
+ Before we continue, you should understand the basic
+ POSTGRES system architecture. Understanding how the
+ parts of POSTGRES interact will make the next chapter
+ somewhat clearer.
+ In database jargon, POSTGRES uses a simple "process
+ per-user" client/server model. A POSTGRES session
+ consists of the following cooperating UNIX processes (programs):
+<UL>
+ <LI>A supervisory daemon process (the <B>postmaster</B>),
+ <LI>the user's frontend application (e.g., the <B>psql</B> program), and
+ <LI>the one or more backend database servers (the <B>postgres</B> process itself).
+</UL>
+ A single <B>postmaster</B> manages a given collection of
+ databases on a single host. Such a collection of
+ databases is called an installation or site. Frontend
+ applications that wish to access a given database
+ within an installation make calls to the library.
+ The library sends user requests over the network to the
+ <B>postmaster</B> (Figure 1(a)), which in turn starts a new
+ backend server process (Figure 1(b))
+
+ <IMG SRC="figure01.gif" ALIGN=right ALT="Figure 1- How a connection is established"><br>
+
+ and connects the
+ frontend process to the new server (Figure 1(c)). From
+ that point on, the frontend process and the backend
+ server communicate without intervention by the
+ <B>postmaster</B>. Hence, the <B>postmaster</B> is always running, waiting
+ for requests, whereas frontend and backend processes
+ come and go. The <B>LIBPQ</B> library allows a single
+ frontend to make multiple connections to backend processes.
+ However, the frontend application is still a
+ single-threaded process. Multithreaded frontend/backend
+ connections are not currently supported in <B>LIBPQ</B>.
+ One implication of this architecture is that the
+ <B>postmaster</B> and the backend always run on the same
+ machine (the database server), while the frontend
+ application may run anywhere. You should keep this
+ in mind,
+ because the files that can be accessed on a client
+ machine may not be accessible (or may only be accessed
+ using a different filename) on the database server
+ machine.
+ You should also be aware that the <B>postmaster</B> and
+ postgres servers run with the user-id of the POSTGRES
+ "superuser." Note that the POSTGRES superuser does not
+ have to be a special user (e.g., a user named
+ "postgres"). Furthermore, the POSTGRES superuser
+ should
+ definitely not be the UNIX superuser, "root"! In any
+ case, all files relating to a database should belong to
+ this POSTGRES superuser.
+
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="intro.html">[ Previous ]</A>
+<A HREF="start.html">[ Next ]</A>
+</font>
+</BODY>
+</HTML>
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+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 - Copyright</TITLE>
+</HEAD>
+
+<BODY>
+<H1 align=center>The <B>POSTGRES95</B> - Copyright</H1>
+<HR>
+ <B>POSTGRES95</B> is copyright (C) 1994-5 by the Regents of the
+University of California. Permission to use, copy, modify,
+and distribute this software and its documentation for any
+purpose, without fee, and without a written agreement is
+hereby granted, provided that the above copyright notice and
+this paragraph and the following two paragraphs appear in
+all copies.<p>
+<b> IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE
+ LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL,
+ INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST
+ PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND
+ ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA
+ HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ THE UNIVERSITY OF CALIFORNIA SPECIFICALLY
+ DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED
+ HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF
+ CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
+ SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+</b>
+
+</BODY>
+</HTML>
--- /dev/null
+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - EXTENDING SQL: AN OVERVIEW</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="advanced.html">[ Previous ]</A>
+<A HREF="xfunc.html">[ Next ]</A>
+</font>
+<HR>
+
+<H1>6. EXTENDING SQL: AN OVERVIEW</H1>
+<HR>
+ In the sections that follow, we will discuss how you
+ can extend the POSTGRES <B>SQL</B> query language by adding:
+ <UL>
+ <LI>functions
+ <LI>types
+ <LI>operators
+ <LI>aggregates
+ </UL>
+<p>
+<H2><A NAME="how-extensibility-works">6.1. How Extensibility Works</A></H2>
+ POSTGRES is extensible because its operation is
+ catalog-driven. If you are familiar with standard
+ relational systems, you know that they store information
+ about databases, tables, columns, etc., in what are
+ commonly known as system catalogs. (Some systems call
+ this the data dictionary). The catalogs appear to the
+ user as classes, like any other, but the DBMS stores
+ its internal bookkeeping in them. One key difference
+ between POSTGRES and standard relational systems is
+ that POSTGRES stores much more information in its
+ catalogs -- not only information about tables and columns,
+ but also information about its types, functions, access
+ methods, and so on. These classes can be modified by
+ the user, and since POSTGRES bases its internal operation
+ on these classes, this means that POSTGRES can be
+ extended by users. By comparison, conventional
+ database systems can only be extended by changing hardcoded
+ procedures within the DBMS or by loading modules
+ specially-written by the DBMS vendor.
+ POSTGRES is also unlike most other data managers in
+ that the server can incorporate user-written code into
+ itself through dynamic loading. That is, the user can
+ specify an object code file (e.g., a compiled .o file
+ or shared library) that implements a new type or function
+ and POSTGRES will load it as required. Code written
+ in <B>SQL</B> are even more trivial to add to the server.
+ This ability to modify its operation "on the fly" makes
+ POSTGRES uniquely suited for rapid prototyping of new
+ applications and storage structures.
+
+<H2><A NAME="the-postgres-type-system">6.2. The POSTGRES Type System</A></H2>
+ The POSTGRES type system can be broken down in several
+ ways.
+ Types are divided into base types and composite types.
+ Base types are those, like <CODE>int4</CODE>, that are implemented
+ in a language such as <B>C</B>. They generally correspond to
+ what are often known as "abstract data types"; POSTGRES
+ can only operate on such types through methods provided
+ by the user and only understands the behavior of such
+ types to the extent that the user describes them.
+ Composite types are created whenever the user creates a
+ class. EMP is an example of a composite type.
+ POSTGRES stores these types in only one way (within the
+ file that stores all instances of the class) but the
+ user can "look inside" at the attributes of these types
+ from the query language and optimize their retrieval by
+ (for example) defining indices on the attributes.
+ POSTGRES base types are further divided into built-in
+ types and user-defined types. Built-in types (like
+ <CODE>int4</CODE>) are those that are compiled into the system.
+ User-defined types are those created by the user in the
+ manner to be described below.
+
+<H2><A NAME="about-the-postgres-system-catalogs">6.3. About the POSTGRES System Catalogs</A></H2>
+ Having introduced the basic extensibility concepts, we
+ can now take a look at how the catalogs are actually
+ laid out. You can skip this section for now, but some
+ later sections will be incomprehensible without the
+ information given here, so mark this page for later
+ reference.
+ All system catalogs have names that begin with <CODE>pg_</CODE>.
+ The following classes contain information that may be
+ useful to the end user. (There are many other system
+ catalogs, but there should rarely be a reason to query
+ them directly.)
+ <p>
+<center>
+<table border=1>
+<tr>
+ <th>catalog name</th><th> description </th>
+</tr>
+<tr>
+ <td><CODE>pg_database</CODE> </td><td> databases </td>
+</tr>
+<tr>
+ <td><CODE>pg_class</CODE> </td><td> classes </td>
+</tr>
+<tr>
+ <td><CODE>pg_attribute</CODE> </td><td> class attributes </td>
+ </tr>
+<tr>
+ <td><CODE>pg_index</CODE> </td><td> secondary indices </td>
+</tr>
+<tr>
+</tr>
+<tr>
+ <td><CODE>pg_proc</CODE> </td><td> procedures (both C and SQL) </td>
+</tr>
+<tr>
+ <td><CODE>pg_type</CODE> </td><td> types (both base and complex) </td>
+</tr>
+<tr>
+ <td><CODE>pg_operator</CODE> </td><td> operators </td>
+</tr>
+<tr>
+ <td><CODE>pg_aggregate</CODE> </td><td> aggregates and aggregate functions </td>
+</tr>
+<tr>
+</tr>
+<tr>
+</tr>
+<tr>
+ <td><CODE>pg_am</CODE> </td><td> access methods </td>
+</tr>
+<tr>
+ <td><CODE>pg_amop</CODE> </td><td> access method operators </td>
+</tr>
+<tr>
+ <td><CODE>pg_amproc</CODE> </td><td> access method support functions </td>
+</tr>
+<tr>
+ <td><CODE>pg_opclass</CODE> </td><td> access method operator classes </td>
+</tr>
+</table>
+</center>
+
+<p>
+ <IMG SRC="figure03.gif"
+ ALT="Figure 3. The major POSTGRES system catalogs">
+ The Reference Manual gives a more detailed explanation
+ of these catalogs and their attributes. However, Figure 3
+ shows the major entities and their relationships
+ in the system catalogs. (Attributes that do not refer
+ to other entities are not shown unless they are part of
+ a primary key.)
+ This diagram is more or less incomprehensible until you
+ actually start looking at the contents of the catalogs
+ and see how they relate to each other. For now, the
+ main things to take away from this diagram are as follows:
+
+ <OL>
+ <LI> In several of the sections that follow, we will
+ present various join queries on the system
+ catalogs that display information we need to extend
+ the system. Looking at this diagram should make
+ some of these join queries (which are often
+ three- or four-way joins) more understandable,
+ because you will be able to see that the
+ attributes used in the queries form foreign keys
+ in other classes.
+ <LI> Many different features (classes, attributes,
+ functions, types, access methods, etc.) are
+ tightly integrated in this schema. A simple
+ create command may modify many of these catalogs.
+ <LI> Types and procedures <A HREF="#6"><font size=-1>[6]</font></A>
+ are central to the schema.
+ Nearly every catalog contains some reference to
+ instances in one or both of these classes. For
+ example, POSTGRES frequently uses type
+ signatures (e.g., of functions and operators) to
+ identify unique instances of other catalogs.
+ <LI> There are many attributes and relationships that
+ have obvious meanings, but there are many
+ (particularly those that have to do with access
+ methods) that do not. The relationships between
+ <CODE>pg_am, pg_amop, pg_amproc, pg_operator</CODE> and
+ <CODE>pg_opclass</CODE> are particularly hard to understand
+ and will be described in depth (in the section
+ on interfacing types and operators to indices)
+ after we have discussed basic extensions.
+</OL>
+<p>
+<HR>
+<A NAME="6"><B>6.</B></A> We use the words <I>procedure</I> and <I>function</I> more or less
+interchangably.
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="advanced.html">[ Previous ]</A>
+<A HREF="xfunc.html">[ Next ]</A>
+</font>
+</BODY>
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+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - Introduction</TITLE>
+</HEAD>
+
+<BODY>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+[ Previous ]
+<A HREF="architec.html">[ Next ]</A>
+</font>
+<HR>
+<H1>1. INTRODUCTION</H1>
+<HR>
+ This document is the user manual for the
+ <A HREF="http://s2k-ftp.cs.berkeley.edu:8000/postgres95/"><B>POSTGRES95</B></A>
+ database management system developed at the University
+ of California at Berkeley. <B>POSTGRES95</B> is based on
+ <A HREF="http://s2k-ftp.CS.Berkeley.EDU:8000/postgres/postgres.html">
+ <B>POSTGRES release 4.2</B></A>. The POSTGRES project,
+ led by Professor Michael Stonebraker, has been sponsored by the
+ Defense Advanced Research Projects Agency (DARPA), the
+ Army Research Office (ARO), the National Science
+ Foundation (NSF), and ESL, Inc.
+<H2>1.1. What is POSTGRES?</H2>
+ Traditional relational database management systems
+ (DBMSs) support a data model consisting of a collection
+ of named relations, containing attributes of a specific
+ type. In current commercial systems, possible types
+ include floating point numbers, integers, character
+ strings, money, and dates. It is commonly recognized
+ that this model is inadequate for future data
+ processing applications.
+ The relational model successfully replaced previous
+ models in part because of its "Spartan simplicity".
+ However, as mentioned, this simplicity often makes the
+ implementation of certain applications very difficult
+ to implement. POSTGRES offers substantial additional
+ power by incorporating the following four additional
+ basic constructs in such a way that users can easily
+ extend the system:
+<p>
+<PRE> classes
+ inheritance
+ types
+ functions
+</PRE><p>
+ In addition, POSTGRES supports a powerful production
+ rule system.
+
+<H2><A NAME="a-short-history-of-the-postgres-project">1.2. A Short History of the POSTGRES Project</A></H2>
+ Implementation of the POSTGRES DBMS began in 1986. The
+ initial concepts for the system were presented in
+ <A HREF="refs.html#STON86">[STON86]</A> and the definition of the initial data model
+ appeared in <A HREF="refs.html#ROW87">[ROWE87]</A>. The design of the rule system at
+ that time was described in <A HREF="refs.html#STON87a">[STON87a]</A>. The rationale
+ and architecture of the storage manager were detailed
+ in <A HREF="refs.html#STON87b">[STON87b]</A>.
+ POSTGRES has undergone several major releases since
+ then. The first "demoware" system became operational
+ in 1987 and was shown at the 1988 <B>ACM-SIGMOD</B>
+ Conference. We released Version 1, described in <A HREF="refs.html#STON90a">[STON90a]</A>,
+ to a few external users in June 1989. In response to a
+ critique of the first rule system <A HREF="refs.html#STON89">[STON89]</A>, the rule
+ system was redesigned <A HREF="refs.html#STON90">[STON90b]</A> and Version 2 was
+ released in June 1990 with the new rule system.
+ Version 3 appeared in 1991 and added support for multiple
+ storage managers, an improved query executor, and a
+ rewritten rewrite rule system. For the most part,
+ releases since then have focused on portability and
+ reliability.
+ POSTGRES has been used to implement many different
+ research and production applications. These include: a
+ financial data analysis system, a jet engine
+ performance monitoring package, an asteroid tracking
+ database, a medical information database, and several
+ geographic information systems. POSTGRES has also been
+ used as an educational tool at several universities.
+ Finally, <A HREF="http://www.illustra.com/">Illustra Information Technologies</A> picked up
+ the code and commercialized it.
+ POSTGRES became the primary data manager for the
+ <A HREF="http://www.sdsc.edu/0/Parts_Collabs/S2K/s2k_home.html">Sequoia 2000</A> scientific computing project in late 1992.
+ Furthermore, the size of the external user community
+ nearly doubled during 1993. It became increasingly
+ obvious that maintenance of the prototype code and
+ support was taking up large amounts of time that should
+ have been devoted to database research. In an effort
+ to reduce this support burden, the project officially
+ ended with <B>Version 4.2</B>.
+
+<H2><A NAME="what-is-postgres95">1.3. What is <B>POSTGRES95</B>?</A></H2>
+ <B>POSTGRES95</B> is a derivative of the last official release
+ of POSTGRES (version 4.2). The code is now completely
+ ANSI C and the code size has been trimmed by 25%. There
+ are a lot of internal changes that improve performance
+ and code maintainability. <B>POSTGRES95</B> runs about 30-50%
+ faster on the Wisconsin Benchmark compared to v4.2.
+ Apart from bug fixes, these are the major enhancements:
+<UL>
+ <LI>The query language <B>POSTQUEL</B> has been replaced with
+ <B>SQL</B> (implemented in the server). We do not support
+ subqueries (which can be imitated with user defined
+ <B>SQL</B> functions) at the moment. Aggregates have been
+ re-implemented. We also added support for <B>GROUP BY</B>.
+ The <B>libpq</B> interface is still available for <B>C</B>
+ programs.
+ <LI>In addition to the monitor program, we provide a new
+ program (<B>psql</B>) which supports <B>GNU</B> <B>readline</B>.
+ <LI>We added a new front-end library, <B>libpgtcl</B>, that
+ supports <B>Tcl</B>-based clients. A sample shell,
+ pgtclsh, provides new Tcl commands to interface <B>tcl</B>
+ programs with the <B>POSTGRES95</B> backend.
+ <LI>The large object interface has been overhauled. We
+ kept Inversion large objects as the only mechanism
+ for storing large objects. (This is not to be
+ confused with the Inversion file system which has been
+ removed.)
+ <LI>The instance-level rule system has been removed.
+ <LI>Rules are still available as rewrite rules.
+ <LI>A short tutorial introducing regular <B>SQL</B> features as
+ well as those of ours is distributed with the source
+ code.
+ <LI><B>GNU</B> make (instead of <B>BSD</B> make) is used for the
+ build. Also, <B>POSTGRES95</B> can be compiled with an
+ unpatched <B>gcc</B> (data alignment of doubles has been
+ fixed).
+</UL>
+<p>
+<H2><A NAME="about-this-release">1.4. About This Release</A></H2>
+ <B>POSTGRES95</B> is available free of charge. This manual
+ describes version 1.0 of <B>POSTGRES95</B>. The authors have
+ compiled and tested <B>POSTGRES95</B> on the following
+ platforms:
+<p>
+<center>
+<table border=4>
+ <tr>
+ <th>Architecture</th>
+ <th>Processor</th>
+ <th>Operating System</th>
+ </tr>
+ <tr>
+ <td>DECstation 3000</td>
+ <td>Alpha AXP</td>
+ <td>OSF/1 2.1, 3.0, 3.2</td>
+ </tr>
+ <tr>
+ <td>DECstation 5000</td>
+ <td>MIPS</td>
+ <td>ULTRIX 4.4</td>
+ </tr>
+ <tr>
+ <td>Sun4</td>
+ <td>SPARC</td>
+ <td>SunOS 4.1.3, 4.1.3_U1; Solaris 2.4</td>
+ </tr>
+ <tr>
+ <td>H-P 9000/700 and 800</td>
+ <td>PA-RISC</td>
+ <td>HP-UX 9.00, 9.01, 9.03</td>
+ </tr>
+ <tr>
+ <td>Intel</td>
+ <td>X86</td>
+ <td>Linux 1.2.8, ELF</td>
+</table>
+</center>
+<p>
+<H2><A NAME="outline-of-this-manual">1.5. Outline of This Manual</A></H2>
+ From now on, We will use POSTGRES to mean <B>POSTGRES95</B>.
+ The first part of this manual goes over some basic sys-
+ tem concepts and procedures for starting the POSTGRES
+ system. We then turn to a tutorial overview of the
+ POSTGRES data model and SQL query language, introducing
+ a few of its advanced features. Next, we explain the
+ POSTGRES approach to extensibility and describe how
+ users can extend POSTGRES by adding user-defined types,
+ operators, aggregates, and both query language and pro-
+ gramming language functions. After an extremely brief
+ overview of the POSTGRES rule system, the manual
+ concludes with a detailed appendix that discusses some of
+ the more involved and operating system-specific
+ procedures involved in extending the system.
+<HR>
+<B>UNIX</B> is a trademark of X/Open, Ltd. Sun4, SPARC, SunOS
+and Solaris are trademarks of Sun Microsystems, Inc. DEC,
+DECstation, Alpha AXP and ULTRIX are trademarks of Digital
+Equipment Corp. PA-RISC and HP-UX are trademarks of
+Hewlett-Packard Co. OSF/1 is a trademark of the Open
+Software Foundation.<p>
+
+ We assume proficiency with UNIX and C programming.
+
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+[ Previous ]
+<A HREF="architec.html">[ Next ]</A>
+</font>
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+ <TITLE>The POSTGRES95 User Manual - LIBPQ</TITLE>
+</HEAD>
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+<HR>
+<H1>12. <B>LIBPQ</B></H1>
+<HR>
+ <B>LIBPQ</B> is the application programming interface to POSTGRES.
+ <B>LIBPQ</B> is a set of library routines which allows
+ client programs to pass queries to the POSTGRES backend
+ server and to receive the results of these queries.
+ This version of the documentation describes the <B>C</B>
+ interface library. Three short programs are included
+ at the end of this section to show how to write programs that use <B>LIBPQ</B>.
+ There are several examples of <B>LIBPQ</B> applications in the
+ following directories:
+
+<pre> ../src/test/regress
+ ../src/test/examples
+ ../src/bin/psql
+</pre>
+ Frontend programs which use <B>LIBPQ</B> must include the
+ header file <CODE>libpq-fe.h</CODE> and must link with the <B>libpq</B>
+ library.
+
+<H2><A NAME="control-and-initialization">12.1. Control and Initialization</A></H2>
+ The following environment variables can be used to set
+ up default environment values to avoid hard-coding
+ database names into an application program:
+
+<UL>
+ <LI><B>PGHOST</B> sets the default server name.
+ <LI><B>PGOPTIONS</B> sets additional runtime options for the POSTGRES backend.
+ <LI><B>PGPORT</B> sets the default port for communicating with the POSTGRES backend.
+ <LI><B>PGTTY</B> sets the file or tty on which debugging messages from the backend server are displayed.
+ <LI><B>PGDATABASE</B> sets the default POSTGRES database name.
+ <LI><B>PGREALM</B> sets the Kerberos realm to use with POSTGRES, if it is different from the local realm. If
+ <LI><B>PGREALM</B> is set, POSTGRES applications will attempt
+ authentication with servers for this realm and use
+ separate ticket files to avoid conflicts with local
+ ticket files. This environment variable is only
+ used if Kerberos authentication is enabled.
+</UL>
+
+<H2><A NAME="database-connection-functions">12.2. Database Connection Functions</A></H2>
+ The following routines deal with making a connection to
+ a backend from a <B>C</B> program.
+
+ <DL>
+ <DT><B>PQsetdb</B>
+ <DD>Makes a new connection to a backend.
+<pre> PGconn *PQsetdb(char *pghost,
+ char *pgport,
+ char *pgoptions,
+ char *pgtty,
+ char *dbName);
+</pre>
+ <DD>If any argument is NULL, then the corresponding
+ environment variable is checked. If the environment variable is also not set, then hardwired
+ defaults are used.
+ <DD>PQsetdb always returns a valid PGconn pointer.
+ <DD>The PQstatus (see below) command should be called
+ to ensure that a connection was properly made
+ before queries are sent via the connection. <B>LIBPQ</B>
+ programmers should be careful to maintain the
+ <DD>PGconn abstraction. Use the accessor functions
+ below to get at the contents of PGconn. Avoid
+ directly referencing the fields of the PGconn
+ structure as they are subject to change in the
+ future.<br>
+ <DT><B>PQdb</B>
+ <DD>Returns the database name of the connection.
+<pre> char *PQdb(PGconn *conn)
+</pre><br>
+ <DT><B>PQhost</B>
+ <DD>Returns the host name of the connection.
+<pre> char *PQhost(PGconn *conn)
+</pre><br>
+ <DT><B>PQoptions</B>
+ <DD>Returns the pgoptions used in the connection.
+<pre> char *PQoptions(PGconn *conn)
+</pre><br>
+ <DT><B>PQport</B>
+ <DD>Returns the pgport of the connection.
+<pre> char *PQport(PGconn *conn)
+</pre><br>
+ <DT><B>PQtty</B>
+ <DD>Returns the pgtty of the connection.
+<pre> char *PQtty(PGconn *conn)
+</pre><br>
+ <DT><B>PQstatus</B>
+ <DD>Returns the status of the connection.
+ <DD>The status can be CONNECTION_OK or CONNECTION_BAD.
+<pre> ConnStatusType *PQstatus(PGconn *conn)
+</pre><br>
+ <DT><B>PQerrorMessage</B>
+ <DD>Returns the error message associated with the connection
+<pre> char *PQerrorMessage(PGconn* conn);
+</pre><br>
+
+ <DT><B>PQfinish</B>
+ <DD>Close the connection to the backend. Also frees
+ memory used by the PGconn structure. The PGconn
+ pointer should not be used after PQfinish has been
+ called.
+<pre> void PQfinish(PGconn *conn)
+</pre><br>
+ <DT><B>PQreset</B>
+ <DD>Reset the communication port with the backend.
+ This function will close the IPC socket connection
+ to the backend and attempt to reestablish a new
+ connection to the same backend.
+<pre> void PQreset(PGconn *conn)
+</pre><br>
+ <DT><B>PQtrace</B>
+ <DD>Enables tracing of messages passed between the
+ frontend and the backend. The messages are echoed
+ to the debug_port file stream.
+<pre> void PQtrace(PGconn *conn,
+ FILE* debug_port);
+</pre><br>
+ <DT><B>PQuntrace</B>
+ <DD>Disables tracing of messages passed between the
+ frontend and the backend.
+<pre> void PQuntrace(PGconn *conn);
+</pre><br>
+</DL>
+<H2><A NAME="query-execution-functions">12.3. Query Execution Functions</A></H2>
+<DL>
+ <DT><B>PQexec</B>
+ <DD>Submit a query to POSTGRES. Returns a PGresult
+ pointer if the query was successful or a NULL otherwise. If a NULL is returned, PQerrorMessage can
+ be used to get more information about the error.
+<pre> PGresult *PQexec(PGconn *conn,
+ char *query);
+</pre>
+ <DD>The <B>PGresult</B> structure encapsulates the query
+ result returned by the backend. <B>LIBPQ</B> programmers
+ should be careful to maintain the PGresult
+ abstraction. Use the accessor functions described
+ below to retrieve the results of the query. Avoid
+ directly referencing the fields of the PGresult
+ structure as they are subject to change in the
+ future.<br>
+ <DT><B>PQresultStatus</B>
+ <DD>Returns the result status of the query. PQresultStatus can return one of the following values:
+<pre> PGRES_EMPTY_QUERY,
+ PGRES_COMMAND_OK, /* the query was a command */
+ PGRES_TUPLES_OK, /* the query successfully returned tuples */
+ PGRES_COPY_OUT,
+ PGRES_COPY_IN,
+ PGRES_BAD_RESPONSE, /* an unexpected response was received */
+ PGRES_NONFATAL_ERROR,
+ PGRES_FATAL_ERROR
+</pre>
+ <DD>If the result status is PGRES_TUPLES_OK, then the
+ following routines can be used to retrieve the
+ tuples returned by the query.<br>
+ <DT><B>PQntuples</B> returns the number of tuples (instances)
+ in the query result.
+
+<pre> int PQntuples(PGresult *res);
+</pre><br>
+ <DT><B>PQnfields</B>
+ <DD>Returns the number of fields
+ (attributes) in the query result.
+
+<pre> int PQnfields(PGresult *res);
+</pre><br>
+ <DT><B>PQfname</B>
+ <DD>Returns the field (attribute) name associated with the given field index. Field indices
+ start at 0.
+
+<pre> char *PQfname(PGresult *res,
+ int field_index);
+</pre><br>
+ <DT><B>PQfnumber</B>
+ <DD>Returns the field (attribute) index
+ associated with the given field name.
+
+<pre> int PQfnumber(PGresult *res,
+ char* field_name);
+</pre><br>
+ <DT><B>PQftype</B>
+ <DD>Returns the field type associated with the
+ given field index. The integer returned is an
+ internal coding of the type. Field indices start
+ at 0.
+
+<pre> Oid PQftype(PGresult *res,
+ int field_num);
+</pre><br>
+ <DT><B>PQfsize</B>
+ <DD>Returns the size in bytes of the field
+ associated with the given field index. If the size
+ returned is -1, the field is a variable length
+ field. Field indices start at 0.
+
+<pre> int2 PQfsize(PGresult *res,
+ int field_index);
+</pre><br>
+ <DT><B>PQgetvalue</B>
+ <DD>Returns the field (attribute) value.
+ For most queries, the value returned by PQgetvalue
+ is a null-terminated ASCII string representation
+ of the attribute value. If the query was a result
+ of a <B>BINARY</B> cursor, then the value returned by
+ PQgetvalue is the binary representation of the
+ type in the internal format of the backend server.
+ It is the programmer's responsibility to cast and
+ convert the data to the correct C type. The value
+ returned by PQgetvalue points to storage that is
+ part of the PGresult structure. One must explicitly
+ copy the value into other storage if it is to
+ be used past the lifetime of the PGresult structure itself.
+
+<pre> char* PQgetvalue(PGresult *res,
+ int tup_num,
+ int field_num);
+</pre><br>
+ <DT><B>PQgetlength</B>
+ <DD>Returns the length of a field
+ (attribute) in bytes. If the field is a struct
+ varlena, the length returned here does not include
+ the size field of the varlena, i.e., it is 4 bytes
+ less.
+<pre> int PQgetlength(PGresult *res,
+ int tup_num,
+ int field_num);
+</pre><br>
+ <DT><B>PQcmdStatus</B>
+ Returns the command status associated with the
+ last query command.
+<pre>
+ char *PQcmdStatus(PGresult *res);
+</pre><br>
+ <DT><B>PQoidStatus</B>
+ Returns a string with the object id of the tuple
+ inserted if the last query is an INSERT command.
+ Otherwise, returns an empty string.
+<pre> char* PQoidStatus(PGresult *res);
+</pre><br>
+ <DT><B>PQprintTuples</B>
+ Prints out all the tuples and, optionally, the
+ attribute names to the specified output stream.
+ The programs psql and monitor both use PQprintTuples for output.
+
+<pre> void PQprintTuples(
+ PGresult* res,
+ FILE* fout, /* output stream */
+ int printAttName,/* print attribute names or not*/
+ int terseOutput, /* delimiter bars or not?*/
+ int width /* width of column, variable width if 0*/
+ );
+</pre><br>
+
+ <DT><B>PQclear</B>
+ Frees the storage associated with the PGresult.
+ Every query result should be properly freed when
+ it is no longer used. Failure to do this will
+ result in memory leaks in the frontend application.
+<pre> void PQclear(PQresult *res);
+</pre><br>
+</DL>
+<H2><A NAME="fast-path">12.4. Fast Path</A></H2>
+ POSTGRES provides a fast path interface to send function calls to the backend. This is a trapdoor into
+ system internals and can be a potential security hole.
+ Most users will not need this feature.
+
+<pre> PGresult* PQfn(PGconn* conn,
+ int fnid,
+ int *result_buf,
+ int *result_len,
+ int result_is_int,
+ PQArgBlock *args,
+ int nargs);
+</pre><br>
+
+ The fnid argument is the object identifier of the function to be executed. result_buf is the buffer in which
+ to load the return value. The caller must have allocated sufficient space to store the return value. The
+ result length will be returned in the storage pointed
+ to by result_len. If the result is to be an integer
+ value, than result_is_int should be set to 1; otherwise
+ it should be set to 0. args and nargs specify the
+ arguments to the function.
+<pre> typedef struct {
+ int len;
+ int isint;
+ union {
+ int *ptr;
+ int integer;
+ } u;
+ } PQArgBlock;
+</pre>
+ PQfn always returns a valid PGresult*. The resultStatus should be checked before the result is used. The
+ caller is responsible for freeing the PGresult with
+ PQclear when it is not longer needed.
+<H2><A NAME="asynchronous-notification">12.5. Asynchronous Notification</A></H2>
+ POSTGRES supports asynchronous notification via the
+ LISTEN and NOTIFY commands. A backend registers its
+ interest in a particular relation with the LISTEN command. All backends listening on a particular relation
+ will be notified asynchronously when a NOTIFY of that
+ relation name is executed by another backend. No
+ additional information is passed from the notifier to
+ the listener. Thus, typically, any actual data that
+ needs to be communicated is transferred through the
+ relation.
+ <B>LIBPQ</B> applications are notified whenever a connected
+ backend has received an asynchronous notification.
+ However, the communication from the backend to the
+ frontend is not asynchronous. Notification comes
+ piggy-backed on other query results. Thus, an application must submit queries, even empty ones, in order to
+ receive notice of backend notification. In effect, the
+ <B>LIBPQ</B> application must poll the backend to see if there
+ is any pending notification information. After the
+ execution of a query, a frontend may call PQNotifies to
+ see if any notification data is available from the
+ backend.
+<DL>
+ <DT><B>PQNotifies</B>
+ <DD>returns the notification from a list of unhandled
+ notifications from the backend. Returns NULL if
+ there are no pending notifications from the backend. PQNotifies behaves like the popping of a
+ stack. Once a notification is returned from PQnotifies, it is considered handled and will be
+ removed from the list of notifications.
+<pre> PGnotify* PQNotifies(PGconn *conn);
+</pre><br>
+</DL>
+ The second sample program gives an example of the use
+ of asynchronous notification.
+<H2><A NAME="functions-associated-with-the-copy-command">12.6. Functions Associated with the COPY Command</A></H2>
+ The copy command in POSTGRES has options to read from
+ or write to the network connection used by <B>LIBPQ</B>.
+ Therefore, functions are necessary to access this network connection directly so applications may take full
+ advantage of this capability.
+<DL>
+ <DT><B>PQgetline</B>
+ <DD>Reads a newline-terminated line of characters
+ (transmitted by the backend server) into a buffer
+ string of size length. Like fgets(3), this routine copies up to length-1 characters into string.
+ It is like gets(3), however, in that it converts
+ the terminating newline into a null character.
+ PQgetline returns EOF at EOF, 0 if the entire line
+ has been read, and 1 if the buffer is full but the
+ terminating newline has not yet been read.
+ Notice that the application must check to see if a
+ new line consists of the single character ".",
+ which indicates that the backend server has finished sending the results of the copy command.
+ Therefore, if the application ever expects to
+ receive lines that are more than length-1 characters long, the application must be sure to check
+ the return value of PQgetline very carefully.
+ The code in
+
+<pre> ../src/bin/psql/psql.c
+</pre>
+ contains routines that correctly handle the copy
+ protocol.
+<pre> int PQgetline(PGconn *conn,
+ char *string,
+ int length)
+</pre><br>
+ <DT><B>PQputline</B>
+ <DD>Sends a null-terminated string to the backend
+ server.
+ The application must explicitly send the single
+ character "." to indicate to the backend that it
+ has finished sending its data.
+
+<pre> void PQputline(PGconn *conn,
+ char *string);
+</pre><br>
+ <DT><B>PQendcopy</B>
+ <DD>Syncs with the backend. This function waits until
+ the backend has finished the copy. It should
+ either be issued when the last string has been
+ sent to the backend using PQputline or when the
+ last string has been received from the backend
+ using PGgetline. It must be issued or the backend
+ may get "out of sync" with the frontend. Upon
+ return from this function, the backend is ready to
+ receive the next query.
+ The return value is 0 on successful completion,
+ nonzero otherwise.
+<pre> int PQendcopy(PGconn *conn);
+</pre><br>
+ As an example:
+<pre> PQexec(conn, "create table foo (a int4, b char16, d float8)");
+ PQexec(conn, "copy foo from stdin");
+ PQputline(conn, "3<TAB>hello world<TAB>4.5\n");
+ PQputline(conn,"4<TAB>goodbye world<TAB>7.11\n");
+ ...
+ PQputline(conn,".\n");
+ PQendcopy(conn);
+</pre><br>
+</DL>
+<H2><A NAME="tracing-functions">12.7. <B>LIBPQ</B> Tracing Functions</A></H2>
+<DL>
+ <DT><B>PQtrace</B>
+ <DD>Enable tracing of the frontend/backend communication to a debugging file stream.
+<pre> void PQtrace(PGconn *conn
+ FILE *debug_port)
+</pre><br>
+
+ <DT><B>PQuntrace</B>
+ <DD>Disable tracing started by PQtrace
+<pre> void PQuntrace(PGconn *conn)
+</pre><br>
+</DL>
+<H2><A NAME="authentication-functions">12.8. User Authentication Functions</A></H2>
+ If the user has generated the appropriate authentication credentials (e.g., obtaining <B>Kerberos</B> tickets),
+ the frontend/backend authentication process is handled
+ by <B>PQexec</B> without any further intervention. The following routines may be called by <B>LIBPQ</B> programs to tailor the behavior of the authentication process.
+<DL>
+ <DT><B>fe_getauthname</B>
+ <DD>Returns a pointer to static space containing whatever name the user has authenticated. Use of this
+ routine in place of calls to getenv(3) or getpwuid(3) by applications is highly recommended, as
+ it is entirely possible that the authenticated
+ user name is not the same as value of the <B>USER</B>
+ environment variable or the user's entry in
+ <CODE>/etc/passwd</CODE>.
+
+<pre> char *fe_getauthname(char* errorMessage)
+</pre><br>
+ <DT><B>fe_setauthsvc</B>
+ <DD>Specifies that <B>LIBPQ</B> should use authentication
+ service name rather than its compiled-in default.
+ <DD>This value is typically taken from a command-line
+ switch.
+<pre> void fe_setauthsvc(char *name,
+ char* errorMessage)
+</pre>
+ <DD>Any error messages from the authentication
+ attempts are returned in the errorMessage argument.
+</DL>
+
+<H2><A NAME="bugs">12.9. BUGS</A></H2>
+ The query buffer is 8192 bytes long, and queries over
+ that length will be silently truncated.
+<H2><A NAME="sample-programs">12.10. Sample Programs</H2>
+<p>
+<H3><A NAME="sample-program-1">12.10.1. Sample Program 1</A></H3>
+<pre>
+ /*
+ * testlibpq.c
+ * Test the C version of LIBPQ, the POSTGRES frontend library.
+ *
+ *
+ */
+ #include <stdio.h>
+ #include "libpq-fe.h"
+<p>
+ void
+ exit_nicely(PGconn* conn)
+ {
+ PQfinish(conn);
+ exit(1);
+ }
+<p>
+ main()
+ {
+ char *pghost, *pgport, *pgoptions, *pgtty;
+ char* dbName;
+ int nFields;
+ int i,j;
+<p>
+ /* FILE *debug; */
+<p>
+ PGconn* conn;
+ PGresult* res;
+<p>
+ /* begin, by setting the parameters for a backend connection
+ if the parameters are null, then the system will try to use
+ reasonable defaults by looking up environment variables
+ or, failing that, using hardwired constants */
+ pghost = NULL; /* host name of the backend server */
+ pgport = NULL; /* port of the backend server */
+ pgoptions = NULL; /* special options to start up the backend server */
+ pgtty = NULL; /* debugging tty for the backend server */
+ dbName = "template1";
+<p>
+ /* make a connection to the database */
+ conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);
+<p>
+ /* check to see that the backend connection was successfully made */
+ if (PQstatus(conn) == CONNECTION_BAD) {
+ fprintf(stderr,"Connection to database '%s' failed.0, dbName);
+ fprintf(stderr,"%s",PQerrorMessage(conn));
+ exit_nicely(conn);
+ }
+<p>
+ /* debug = fopen("/tmp/trace.out","w"); */
+ /* PQtrace(conn, debug); */
+<p>
+ /* start a transaction block */
+
+ res = PQexec(conn,"BEGIN");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"BEGIN command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ /* should PQclear PGresult whenever it is no longer needed to avoid
+ memory leaks */
+ PQclear(res);
+<p>
+ /* fetch instances from the pg_database, the system catalog of databases*/
+ res = PQexec(conn,"DECLARE myportal CURSOR FOR select * from pg_database");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"DECLARE CURSOR command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ PQclear(res);
+<p>
+ res = PQexec(conn,"FETCH ALL in myportal");
+ if (PQresultStatus(res) != PGRES_TUPLES_OK) {
+ fprintf(stderr,"FETCH ALL command didn't return tuples properly0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+<p>
+ /* first, print out the attribute names */
+ nFields = PQnfields(res);
+ for (i=0; i < nFields; i++) {
+ printf("%-15s",PQfname(res,i));
+ }
+ printf("0);
+<p>
+ /* next, print out the instances */
+ for (i=0; i < PQntuples(res); i++) {
+ for (j=0 ; j < nFields; j++) {
+ printf("%-15s", PQgetvalue(res,i,j));
+ }
+ printf("0);
+ }
+<p>
+ PQclear(res);
+<p>
+ /* close the portal */
+ res = PQexec(conn, "CLOSE myportal");
+ PQclear(res);
+<p>
+ /* end the transaction */
+ res = PQexec(conn, "END");
+ PQclear(res);
+<p>
+ /* close the connection to the database and cleanup */
+ PQfinish(conn);
+
+ /* fclose(debug); */
+ }
+</pre>
+<p>
+<H3><A NAME="sample-program-2">12.10.2. Sample Program 2</A></H3>
+<pre>
+ /*
+ * testlibpq2.c
+ * Test of the asynchronous notification interface
+ *
+ populate a database with the following:
+<p>
+ CREATE TABLE TBL1 (i int4);
+<p>
+ CREATE TABLE TBL2 (i int4);
+<p>
+ CREATE RULE r1 AS ON INSERT TO TBL1 DO [INSERT INTO TBL2 values (new.i); NOTIFY TBL2];
+<p>
+ * Then start up this program
+ * After the program has begun, do
+<p>
+ INSERT INTO TBL1 values (10);
+<p>
+ *
+ *
+ */
+ #include <stdio.h>
+ #include "libpq-fe.h"
+<p>
+ void exit_nicely(PGconn* conn)
+ {
+ PQfinish(conn);
+ exit(1);
+ }
+<p>
+ main()
+ {
+ char *pghost, *pgport, *pgoptions, *pgtty;
+ char* dbName;
+ int nFields;
+ int i,j;
+<p>
+ PGconn* conn;
+ PGresult* res;
+ PGnotify* notify;
+<p>
+ /* begin, by setting the parameters for a backend connection
+ if the parameters are null, then the system will try to use
+ reasonable defaults by looking up environment variables
+ or, failing that, using hardwired constants */
+ pghost = NULL; /* host name of the backend server */
+ pgport = NULL; /* port of the backend server */
+ pgoptions = NULL; /* special options to start up the backend server */
+ pgtty = NULL; /* debugging tty for the backend server */
+ dbName = getenv("USER"); /* change this to the name of your test database*/
+<p>
+ /* make a connection to the database */
+ conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);
+
+ /* check to see that the backend connection was successfully made */
+ if (PQstatus(conn) == CONNECTION_BAD) {
+ fprintf(stderr,"Connection to database '%s' failed.0, dbName);
+ fprintf(stderr,"%s",PQerrorMessage(conn));
+ exit_nicely(conn);
+ }
+<p>
+ res = PQexec(conn, "LISTEN TBL2");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"LISTEN command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ /* should PQclear PGresult whenever it is no longer needed to avoid
+ memory leaks */
+ PQclear(res);
+<p>
+ while (1) {
+ /* async notification only come back as a result of a query*/
+ /* we can send empty queries */
+ res = PQexec(conn, " ");
+ /* printf("res->status = %s0, pgresStatus[PQresultStatus(res)]); */
+ /* check for asynchronous returns */
+ notify = PQnotifies(conn);
+ if (notify) {
+ fprintf(stderr,
+ "ASYNC NOTIFY of '%s' from backend pid '%d' received0,
+ notify->relname, notify->be_pid);
+ free(notify);
+ break;
+ }
+ PQclear(res);
+ }
+<p>
+ /* close the connection to the database and cleanup */
+ PQfinish(conn);
+<p>
+ }
+</pre>
+<p>
+<H3><A NAME="sample-program-3">12.10.3. Sample Program 3</A></H3>
+<pre>
+ /*
+ * testlibpq3.c
+ * Test the C version of LIBPQ, the POSTGRES frontend library.
+ * tests the binary cursor interface
+ *
+ *
+ *
+ populate a database by doing the following:
+<p>
+ CREATE TABLE test1 (i int4, d float4, p polygon);
+<p>
+ INSERT INTO test1 values (1, 3.567, '(3.0, 4.0, 1.0, 2.0)'::polygon);
+<p>
+ INSERT INTO test1 values (2, 89.05, '(4.0, 3.0, 2.0, 1.0)'::polygon);
+<p>
+ the expected output is:
+<p>
+ tuple 0: got
+ i = (4 bytes) 1,
+ d = (4 bytes) 3.567000,
+ p = (4 bytes) 2 points boundbox = (hi=3.000000/4.000000, lo = 1.000000,2.000000)
+ tuple 1: got
+ i = (4 bytes) 2,
+ d = (4 bytes) 89.050003,
+ p = (4 bytes) 2 points boundbox = (hi=4.000000/3.000000, lo = 2.000000,1.000000)
+<p>
+ *
+ */
+ #include <stdio.h>
+ #include "libpq-fe.h"
+ #include "utils/geo-decls.h" /* for the POLYGON type */
+<p>
+ void exit_nicely(PGconn* conn)
+ {
+ PQfinish(conn);
+ exit(1);
+ }
+<p>
+ main()
+ {
+ char *pghost, *pgport, *pgoptions, *pgtty;
+ char* dbName;
+ int nFields;
+ int i,j;
+ int i_fnum, d_fnum, p_fnum;
+<p>
+ PGconn* conn;
+ PGresult* res;
+<p>
+ /* begin, by setting the parameters for a backend connection
+ if the parameters are null, then the system will try to use
+ reasonable defaults by looking up environment variables
+ or, failing that, using hardwired constants */
+ pghost = NULL; /* host name of the backend server */
+ pgport = NULL; /* port of the backend server */
+ pgoptions = NULL; /* special options to start up the backend server */
+ pgtty = NULL; /* debugging tty for the backend server */
+<p>
+ dbName = getenv("USER"); /* change this to the name of your test database*/
+<p>
+ /* make a connection to the database */
+ conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);
+<p>
+ /* check to see that the backend connection was successfully made */
+ if (PQstatus(conn) == CONNECTION_BAD) {
+ fprintf(stderr,"Connection to database '%s' failed.0, dbName);
+ fprintf(stderr,"%s",PQerrorMessage(conn));
+ exit_nicely(conn);
+ }
+<p>
+ /* start a transaction block */
+ res = PQexec(conn,"BEGIN");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"BEGIN command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ /* should PQclear PGresult whenever it is no longer needed to avoid
+ memory leaks */
+ PQclear(res);
+<p>
+ /* fetch instances from the pg_database, the system catalog of databases*/
+ res = PQexec(conn,"DECLARE mycursor BINARY CURSOR FOR select * from test1");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"DECLARE CURSOR command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ PQclear(res);
+<p>
+ res = PQexec(conn,"FETCH ALL in mycursor");
+ if (PQresultStatus(res) != PGRES_TUPLES_OK) {
+ fprintf(stderr,"FETCH ALL command didn't return tuples properly0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+<p>
+ i_fnum = PQfnumber(res,"i");
+ d_fnum = PQfnumber(res,"d");
+ p_fnum = PQfnumber(res,"p");
+<p>
+ for (i=0;i<3;i++) {
+ printf("type[%d] = %d, size[%d] = %d0,
+ i, PQftype(res,i),
+ i, PQfsize(res,i));
+ }
+ for (i=0; i < PQntuples(res); i++) {
+ int *ival;
+ float *dval;
+ int plen;
+ POLYGON* pval;
+ /* we hard-wire this to the 3 fields we know about */
+ ival = (int*)PQgetvalue(res,i,i_fnum);
+ dval = (float*)PQgetvalue(res,i,d_fnum);
+ plen = PQgetlength(res,i,p_fnum);
+<p>
+ /* plen doesn't include the length field so need to increment by VARHDSZ*/
+ pval = (POLYGON*) malloc(plen + VARHDRSZ);
+ pval->size = plen;
+ memmove((char*)&pval->npts, PQgetvalue(res,i,p_fnum), plen);
+ printf("tuple %d: got0, i);
+ printf(" i = (%d bytes) %d,0,
+ PQgetlength(res,i,i_fnum), *ival);
+ printf(" d = (%d bytes) %f,0,
+ PQgetlength(res,i,d_fnum), *dval);
+ printf(" p = (%d bytes) %d points boundbox = (hi=%f/%f, lo = %f,%f)0,
+ PQgetlength(res,i,d_fnum),
+ pval->npts,
+ pval->boundbox.xh,
+ pval->boundbox.yh,
+ pval->boundbox.xl,
+ pval->boundbox.yl);
+ }
+<p>
+ PQclear(res);
+<p>
+ /* close the portal */
+ res = PQexec(conn, "CLOSE mycursor");
+ PQclear(res);
+<p>
+ /* end the transaction */
+ res = PQexec(conn, "END");
+ PQclear(res);
+<p>
+ /* close the connection to the database and cleanup */
+ PQfinish(conn);
+<p>
+ }
+</pre>
+<HR>
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+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - LARGE OBJECTS</TITLE>
+</HEAD>
+
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+
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+<HR>
+<H1>13. LARGE OBJECTS</H1>
+<HR>
+ In POSTGRES, data values are stored in tuples and
+ individual tuples cannot span data pages. Since the size of
+ a data page is 8192 bytes, the upper limit on the size
+ of a data value is relatively low. To support the storage
+ of larger atomic values, POSTGRES provides a large
+ object interface. This interface provides file
+ oriented access to user data that has been declared to
+ be a large type.
+ This section describes the implementation and the
+ programmatic and query language interfaces to POSTGRES
+ large object data.
+
+<H2><A NAME="historical-note">13.1. Historical Note</A></H2>
+ Originally, <B>POSTGRES 4.2</B> supports three standard
+ implementations of large objects: as files external
+ to POSTGRES, as <B>UNIX</B> files managed by POSTGRES, and as data
+ stored within the POSTGRES database. It causes
+ considerable confusion among users. As a result, we only
+ support large objects as data stored within the POSTGRES
+ database in <B>POSTGRES95</B>. Even though is is slower to
+ access, it provides stricter data integrity and time
+ travel. For historical reasons, they are called
+ Inversion large objects. (We will use Inversion and large
+ objects interchangeably to mean the same thing in this
+ section.)
+
+<H2><A NAME="inversion-large-objects">13.2. Inversion Large Objects</A></H2>
+ The Inversion large object implementation breaks large
+ objects up into "chunks" and stores the chunks in
+ tuples in the database. A B-tree index guarantees fast
+ searches for the correct chunk number when doing random
+ access reads and writes.
+
+<H2><A NAME="large-object-interfaces">13.3. Large Object Interfaces</A></H2>
+ The facilities POSTGRES provides to access large
+ objects, both in the backend as part of user-defined
+ functions or the front end as part of an application
+ using the interface, are described below. (For users
+ familiar with <B>POSTGRES 4.2</B>, <B>POSTGRES95</B> has a new set of
+ functions providing a more coherent interface. The
+ interface is the same for dynamically-loaded C
+ functions as well as for .
+ The POSTGRES large object interface is modeled after
+ the <B>UNIX</B> file system interface, with analogues of
+ <B>open(2), read(2), write(2), lseek(2)</B>, etc. User
+ functions call these routines to retrieve only the data of
+ interest from a large object. For example, if a large
+ object type called mugshot existed that stored
+ photographs of faces, then a function called beard could
+ be declared on mugshot data. Beard could look at the
+ lower third of a photograph, and determine the color of
+ the beard that appeared there, if any. The entire
+ large object value need not be buffered, or even
+ examined, by the beard function.
+ Large objects may be accessed from dynamically-loaded <B>C</B>
+ functions or database client programs that link the
+ library. POSTGRES provides a set of routines that
+ support opening, reading, writing, closing, and seeking on
+ large objects.
+<p>
+<H3><A NAME="creating-large-objects">13.3.1. Creating a Large Object</A></H3>
+ The routine
+<pre> Oid lo_creat(PGconn *conn, int mode)
+</pre>
+ creates a new large object. The mode is a bitmask
+ describing several different attributes of the new
+ object. The symbolic constants listed here are defined
+ in
+<pre> /usr/local/postgres95/src/backend/libpq/libpq-fs.h
+</pre>
+ The access type (read, write, or both) is controlled by
+ OR ing together the bits <B>INV_READ</B> and <B>INV_WRITE</B>. If
+ the large object should be archived -- that is, if
+ historical versions of it should be moved periodically to
+ a special archive relation -- then the <B>INV_ARCHIVE</B> bit
+ should be set. The low-order sixteen bits of mask are
+ the storage manager number on which the large object
+ should reside. For sites other than Berkeley, these
+ bits should always be zero.
+ The commands below create an (Inversion) large object:
+<pre> inv_oid = lo_creat(INV_READ|INV_WRITE|INV_ARCHIVE);
+</pre>
+
+<H3><A NAME="importing-a-large-object">13.3.2. Importing a Large Object</A></H3>
+To import a <B>UNIX</B> file as
+ a large object, call
+<pre> Oid
+ lo_import(PGconn *conn, text *filename)
+</pre>
+ The filename argument specifies the <B>UNIX</B> pathname of
+ the file to be imported as a large object.
+<p>
+<H3><A NAME="exporting-a-large-object">13.3.3. Exporting a Large Object</A></H3>
+To export a large object
+ into <B>UNIX</B> file, call
+<pre> int
+ lo_export(PGconn *conn, Oid lobjId, text *filename)
+</pre>
+ The lobjId argument specifies the Oid of the large
+ object to export and the filename argument specifies
+ the <B>UNIX</B> pathname of the file.
+<p>
+<H3><A NAME="opening-an-existing-large-object">13.3.4. Opening an Existing Large Object</A></H3>
+ To open an existing large object, call
+<pre> int
+ lo_open(PGconn *conn, Oid lobjId, int mode, ...)
+</pre>
+ The lobjId argument specifies the Oid of the large
+ object to open. The mode bits control whether the
+ object is opened for reading INV_READ), writing or
+ both.
+ A large object cannot be opened before it is created.
+ lo_open returns a large object descriptor for later use
+ in lo_read, lo_write, lo_lseek, lo_tell, and lo_close.
+<p>
+<H3><A NAME="writing-data-to-a-large-object">13.3.5. Writing Data to a Large Object</A></H3>
+ The routine
+<pre> int
+ lo_write(PGconn *conn, int fd, char *buf, int len)
+</pre>
+ writes len bytes from buf to large object fd. The fd
+ argument must have been returned by a previous lo_open.
+ The number of bytes actually written is returned. In
+ the event of an error, the return value is negative.
+<p>
+<H3><A NAME="seeking-on-a-large-object">13.3.6. Seeking on a Large Object</A></H3>
+ To change the current read or write location on a large
+ object, call
+<pre> int
+ lo_lseek(PGconn *conn, int fd, int offset, int whence)
+</pre>
+ This routine moves the current location pointer for the
+ large object described by fd to the new location specified
+ by offset. The valid values for .i whence are
+ SEEK_SET SEEK_CUR and SEEK_END.
+<p>
+<H3><A NAME="closing-a-large-object-descriptor">13.3.7. Closing a Large Object Descriptor</A></H3>
+ A large object may be closed by calling
+<pre> int
+ lo_close(PGconn *conn, int fd)
+</pre>
+ where fd is a large object descriptor returned by
+ lo_open. On success, <B>lo_close</B> returns zero. On error,
+ the return value is negative.
+
+<H2><A NAME="built-in-registered-functions">13.4. Built in registered functions</A></H2>
+ There are two built-in registered functions, <B>lo_import</B>
+ and <B>lo_export</B> which are convenient for use in <B>SQL</B>
+ queries.
+ Here is an example of there use
+<pre> CREATE TABLE image (
+ name text,
+ raster oid
+ );
+
+ INSERT INTO image (name, raster)
+ VALUES ('beautiful image', lo_import('/etc/motd'));
+
+ SELECT lo_export(image.raster, "/tmp/motd") from image
+ WHERE name = 'beautiful image';
+</pre>
+<H2><A NAME="accessing-large-objects-from-libpq">13.5. Accessing Large Objects from LIBPQ</A></H2>
+ Below is a sample program which shows how the large object
+ interface
+ in LIBPQ can be used. Parts of the program are
+ commented out but are left in the source for the readers
+ benefit. This program can be found in
+<pre> ../src/test/examples
+</pre>
+ Frontend applications which use the large object interface
+ in LIBPQ should include the header file
+ libpq/libpq-fs.h and link with the libpq library.
+
+<H2><A NAME="sample-program">13.6. Sample Program</A></H2>
+<pre> /*--------------------------------------------------------------
+ *
+ * testlo.c--
+ * test using large objects with libpq
+ *
+ * Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ * /usr/local/devel/pglite/cvs/src/doc/manual.me,v 1.16 1995/09/01 23:55:00 jolly Exp
+ *
+ *--------------------------------------------------------------
+ */
+ #include <stdio.h>
+ #include "libpq-fe.h"
+ #include "libpq/libpq-fs.h"
+<p>
+ #define BUFSIZE 1024
+<p>
+ /*
+ * importFile * import file "in_filename" into database as large object "lobjOid"
+ *
+ */
+ Oid importFile(PGconn *conn, char *filename)
+ {
+ Oid lobjId;
+ int lobj_fd;
+ char buf[BUFSIZE];
+ int nbytes, tmp;
+ int fd;
+<p>
+ /*
+ * open the file to be read in
+ */
+ fd = open(filename, O_RDONLY, 0666);
+ if (fd < 0) { /* error */
+ fprintf(stderr, "can't open unix file
+ }
+<p>
+ /*
+ * create the large object
+ */
+ lobjId = lo_creat(conn, INV_READ|INV_WRITE);
+ if (lobjId == 0) {
+ fprintf(stderr, "can't create large object");
+ }
+<p>
+ lobj_fd = lo_open(conn, lobjId, INV_WRITE);
+ /*
+ * read in from the Unix file and write to the inversion file
+ */
+ while ((nbytes = read(fd, buf, BUFSIZE)) > 0) {
+ tmp = lo_write(conn, lobj_fd, buf, nbytes);
+ if (tmp < nbytes) {
+ fprintf(stderr, "error while reading
+ }
+ }
+<p>
+ (void) close(fd);
+ (void) lo_close(conn, lobj_fd);
+<p>
+ return lobjId;
+ }
+<p>
+ void pickout(PGconn *conn, Oid lobjId, int start, int len)
+ {
+ int lobj_fd;
+ char* buf;
+ int nbytes;
+ int nread;
+<p>
+ lobj_fd = lo_open(conn, lobjId, INV_READ);
+ if (lobj_fd < 0) {
+ fprintf(stderr,"can't open large object %d",
+ lobjId);
+ }
+<p>
+ lo_lseek(conn, lobj_fd, start, SEEK_SET);
+ buf = malloc(len+1);
+<p>
+ nread = 0;
+ while (len - nread > 0) {
+ nbytes = lo_read(conn, lobj_fd, buf, len - nread);
+ buf[nbytes] = ' ';
+ fprintf(stderr,">>> %s", buf);
+ nread += nbytes;
+ }
+ fprintf(stderr,"0);
+ lo_close(conn, lobj_fd);
+ }
+<p>
+ void overwrite(PGconn *conn, Oid lobjId, int start, int len)
+ {
+ int lobj_fd;
+ char* buf;
+ int nbytes;
+ int nwritten;
+ int i;
+<p>
+ lobj_fd = lo_open(conn, lobjId, INV_READ);
+ if (lobj_fd < 0) {
+ fprintf(stderr,"can't open large object %d",
+ lobjId);
+ }
+<p>
+ lo_lseek(conn, lobj_fd, start, SEEK_SET);
+ buf = malloc(len+1);
+<p>
+ for (i=0;i<len;i++)
+ buf[i] = 'X';
+ buf[i] = ' ';
+<p>
+ nwritten = 0;
+ while (len - nwritten > 0) {
+ nbytes = lo_write(conn, lobj_fd, buf + nwritten, len - nwritten);
+ nwritten += nbytes;
+ }
+ fprintf(stderr,"0);
+ lo_close(conn, lobj_fd);
+ }
+<p>
+
+ /*
+ * exportFile * export large object "lobjOid" to file "out_filename"
+ *
+ */
+ void exportFile(PGconn *conn, Oid lobjId, char *filename)
+ {
+ int lobj_fd;
+ char buf[BUFSIZE];
+ int nbytes, tmp;
+ int fd;
+<p>
+ /*
+ * create an inversion "object"
+ */
+ lobj_fd = lo_open(conn, lobjId, INV_READ);
+ if (lobj_fd < 0) {
+ fprintf(stderr,"can't open large object %d",
+ lobjId);
+ }
+<p>
+ /*
+ * open the file to be written to
+ */
+ fd = open(filename, O_CREAT|O_WRONLY, 0666);
+ if (fd < 0) { /* error */
+ fprintf(stderr, "can't open unix file
+ filename);
+ }
+<p>
+ /*
+ * read in from the Unix file and write to the inversion file
+ */
+ while ((nbytes = lo_read(conn, lobj_fd, buf, BUFSIZE)) > 0) {
+ tmp = write(fd, buf, nbytes);
+ if (tmp < nbytes) {
+ fprintf(stderr,"error while writing
+ filename);
+ }
+ }
+<p>
+ (void) lo_close(conn, lobj_fd);
+ (void) close(fd);
+<p>
+ return;
+ }
+<p>
+ void
+ exit_nicely(PGconn* conn)
+ {
+ PQfinish(conn);
+ exit(1);
+ }
+<p>
+ int
+ main(int argc, char **argv)
+ {
+ char *in_filename, *out_filename;
+ char *database;
+ Oid lobjOid;
+ PGconn *conn;
+ PGresult *res;
+<p>
+ if (argc != 4) {
+ fprintf(stderr, "Usage: %s database_name in_filename out_filename0,
+ argv[0]);
+ exit(1);
+ }
+<p>
+ database = argv[1];
+ in_filename = argv[2];
+ out_filename = argv[3];
+<p>
+ /*
+ * set up the connection
+ */
+ conn = PQsetdb(NULL, NULL, NULL, NULL, database);
+<p>
+ /* check to see that the backend connection was successfully made */
+ if (PQstatus(conn) == CONNECTION_BAD) {
+ fprintf(stderr,"Connection to database '%s' failed.0, database);
+ fprintf(stderr,"%s",PQerrorMessage(conn));
+ exit_nicely(conn);
+ }
+<p>
+ res = PQexec(conn, "begin");
+ PQclear(res);
+
+ printf("importing file
+ /* lobjOid = importFile(conn, in_filename); */
+ lobjOid = lo_import(conn, in_filename);
+ /*
+ printf("as large object %d.0, lobjOid);
+<p>
+ printf("picking out bytes 1000-2000 of the large object0);
+ pickout(conn, lobjOid, 1000, 1000);
+<p>
+ printf("overwriting bytes 1000-2000 of the large object with X's0);
+ overwrite(conn, lobjOid, 1000, 1000);
+ */
+<p>
+ printf("exporting large object to file
+ /* exportFile(conn, lobjOid, out_filename); */
+ lo_export(conn, lobjOid,out_filename);
+<p>
+ res = PQexec(conn, "end");
+ PQclear(res);
+ PQfinish(conn);
+ exit(0);
+ }
+</pre>
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="libpq.html">[ Previous ]</A>
+<A HREF="rules.html">[ Next ]</A>
+</font>
+</BODY>
+</HTML>
--- /dev/null
+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual</TITLE>
+</HEAD>
+
+<BODY>
+<H1 align=center>
+The <B>
+<A HREF="http://s2k-ftp.cs.berkeley.edu:8000/postgres95/">
+POSTGRES95</A></B> User Manual</H1>
+
+<p align=CENTER>
+
+ Version 1.0 (September 5, 1995)<br><br>
+
+ <A HREF="http://s2k-ftp.cs.berkeley.edu:8000/personal/andrew">Andrew Yu</A>
+ and
+ <A HREF="http://http.cs.berkeley.edu/~jolly/">Jolly Chen</A><br>
+ (with the POSTGRES Group)<br>
+ Computer Science Div., Dept. of EECS<br>
+ University of California at Berkeley<br>
+</p>
+<!--#exec cgi="/cgi-bin/wais-pg95.pl"-->
+<H1 align=center>Table of Contents</H1>
+<DL>
+ <DT><A HREF="intro.html">1. INTRODUCTION</A>
+ <DL>
+ <DT><A HREF="intro.html#a-short-history-of-the-postgres-project">1.1. A Short History of POSTGRES</A>
+ <DT><A HREF="intro.html#what-is-postgres95">1.2. What is POSTGRES95?</A>
+ <DT><A HREF="intro.html#about-this-release">1.4. About This Release</A>
+ <DT><A HREF="intro.html#outline-of-this-manual">1.5. Outline of This Manual</A>
+ </DL>
+ <DT><A HREF="architec.html">2. ARCHITECTURE CONCEPTS</A>
+ <DT><A HREF="start.html">3. GETTING STARTED</A>
+ <DL>
+ <DT><A HREF="start.html#setting-up-your-environment">3.1. Setting Up Your Enviroment</A>
+ <DT><A HREF="start.html#starting-the-postmaster">3.2. Starting The Postmaster</A>
+ <DT><A HREF="start.html#adding-and-deleting-users">3.3. Adding And Deleting Users</A>
+ <DT><A HREF="start.html#starting-applications">3.4. Starting Applications</A>
+ <DT><A HREF="start.html#managing-a-database">3.5. Managing A Database</A>
+ <DL>
+ <DT><A HREF="start.html#creating-a-database">3.5.1. Creating A Database</A>
+ <DT><A HREF="start.html#accesssing-a-database">3.5.2. Accessing A Database</A>
+ <DT><A HREF="start.html#destroying-a-database">3.5.3. Destroying A Database</A>
+ </DL>
+ </DL>
+ <DT><A HREF="query.html">4. QUERY LANGUAGE</A>
+ <DL>
+ <DT><A HREF="query.html#concepts">4.1. Concepts</A>
+ <DT><A HREF="query.html#creating-a-new-class">4.2. Creating a New Class</A>
+ <DT><A HREF="query.html#populating-a-class-with-instances">4.3. Populating a Class with Instances</A>
+ <DT><A HREF="query.html#querying-a-class">4.4. Querying a Class</A>
+ <DT><A HREF="query.html#redirecting-select-queries">4.5. Redirecting SELECT Queries</A>
+ </DL>
+ <DT><A HREF="advanced.html">5. ADVANCED POSTGRES SQL FEATURES</A>
+ <DL>
+ <DT><A HREF="advanced.html#inheritance">5.1. Inheritance</A>
+ <DT><A HREF="advanced.html#time-travel">5.2. Time Travel</A>
+ <DT><A HREF="advanced.html#non-atomic-values">5.3. Non-Atomic Values</A>
+ <DL>
+ <DT><A HREF="advanced.html#arrays">5.3.1. Arrays</A>
+ </DL>
+ </DL>
+ <DT><A HREF="extend.html">6. EXTENDING SQL: AN OVERVIEW</A>
+ <DL>
+ <DT><A HREF="extend.html#how-extensibility-works">6.1. How Extensibility Works</A>
+ <DT><A HREF="extend.html#the-postgres-type-system">6.2. The POSTGRES Type System</A>
+ <DT><A HREF="extend.html#about-the-postgres-system-catalogs">6.3. About the POSTGRES System Catalogs</A>
+ </DL>
+ <DT><A HREF="xfunc.html">7. EXTENDING SQL: FUNCTIONS</A>
+ <DL>
+ <DT><A HREF="xfunc.html#query-language-sql-functions">7.1. Query Language (SQL) Functions</A>
+ <DL>
+ <DT><A HREF="xfunc.html#sql-functions-on-base-types">7.1.1. SQL Functions on Base Types</A>
+ </DL>
+ <DT><A HREF="xfunc.html#programming-language-functions">7.2. Programming Language Functions</A>
+ <DL>
+ <DT><A HREF="xfunc.html#programming-language-functions-on-base-types">7.2.1. Programming Language Functions on Base Types</A>
+ <DT><A HREF="xfunc.html#programming-language-functions-on-composite-types">7.2.2. Programming Language Functions on Composite Types</A>
+ <DT><A HREF="xfunc.html#caveats">7.2.3. Caveats</A>
+ </DL>
+ </DL>
+ <DT><A HREF="xtypes.html">8. EXTENDING SQL: TYPES</A>
+ <DL>
+ <DT><A HREF="xtypes.html#user-defined-types">8.1. User-Defined Types</A>
+ <DL>
+ <DT><A HREF="xtypes.html#functions-needed-for-a-user-defined-type">8.1.1. Functions Needed for a User-Defined Type</A>
+ <DT><A HREF="xtypes.html#large-objects">8.1.2. Large Objects</A>
+ </DL>
+ </DL>
+ <DT><A HREF="xoper.html">9. EXTENDING SQL: OPERATORS</A>
+ <DL>
+ </DL>
+ <DT><A HREF="xaggr.html">10. EXTENDING SQL: AGGREGATES</A>
+ <DL>
+ </DL>
+ <DT><A HREF="xindex.html">11. INTERFACING EXTENSIONS TO INDICES</A>
+ <DL>
+ </DL>
+ <DT><A HREF="libpq.html">12. LIBPQ</A>
+ <DL>
+ <DT><A HREF="libpq.html#control-and-initialization">12.1. Control and Initialization</A>
+ <DT><A HREF="libpq.html#database-connection-functions">12.2. Database Connection Functions</A>
+ <DT><A HREF="libpq.html#query-execution-functions">12.3. Query Execution Functions</A>
+ <DT><A HREF="libpq.html#fast-path">12.4. Fast Path</A>
+ <DT><A HREF="libpq.html#asynchronous-notification">12.5. Asynchronous Notification</A>
+ <DT><A HREF="libpq.html#functions-associated-with-the-copy-command">12.6. Functions Associated with the COPY Command</A>
+ <DT><A HREF="libpq.html#tracing-functions">12.7. LIBPQ Tracing Functions</A></A>
+ <DT><A HREF="libpq.html#authentication-functions">12.8. User Authentication Functions</A>
+ <DT><A HREF="libpq.html#bugs">12.9. BUGS</A>
+ <DT><A HREF="libpq.html#sample-programs">12.10. Sample Programs</A>
+ <DL>
+ <DT><A HREF="libpq.html#sample-program-1">12.10.1. Sample Program 1</A>
+ <DT><A HREF="libpq.html#sample-program-2">12.10.2. Sample Program 2</A>
+ <DT><A HREF="libpq.html#sample-program-3">12.10.3. Sample Program 3</A>
+ </DL>
+ </DL>
+ <DT><A HREF="lobj.html">13. LARGE OBJECTS</A>
+ <DL>
+ <DT><A HREF="lobj.html#historical-note">13.1. Historical Note</A>
+ <DT><A HREF="lobj.html#inversion-large-objects">13.2. Inversion Large Objects</A>
+ <DT><A HREF="lobj.html#large-object-interfaces">13.3. Large Object Interfaces</A>
+ <DL>
+ <DT><A HREF="lobj.html#creating-large-objects">13.3.1. Creating a Large Object</A>
+ <DT><A HREF="lobj.html#importing-a-large-object">13.3.2. Importing a Large Object</A>
+ <DT><A HREF="lobj.html#exporting-a-large-object">13.3.3. Exporting a Large Object</A>
+ <DT><A HREF="lobj.html#opening-an-existing-large-object">13.3.4. Opening an Existing Large Object</A>
+ <DT><A HREF="lobj.html#writing-data-to-a-large-object">13.3.5. Writing Data to a Large Object</A>
+ <DT><A HREF="lobj.html#seeking-on-a-large-object">13.3.6. Seeking on a Large Object</A>
+ <DT><A HREF="lobj.html#closing-a-large-object-descriptor">13.3.7. Closing a Large Object Descriptor</A>
+ </DL>
+ <DT><A HREF="lobj.html#built-in-registered-functions">13.4. Built in registered functions</A>
+ <DT><A HREF="lobj.html#accessing-large-objects-from-libpq">13.5. Accessing Large Objects from LIBPQ</A>
+ <DT><A HREF="lobj.html#sample-program">13.6. Sample Program</A>
+ </DL>
+ <DT><A HREF="rules.html">14. THE POSTGRES RULE SYSTEM</A>
+ <DT><A HREF="admin.html">15. ADMINISTERING POSTGRES</A>
+ <DT><A HREF="refs.html">16. REFERENCES</A>
+ <p>
+ <DT><A HREF="appenda.html">Appendix A: Linking Dynamically-Loaded Functions</A>
+
+</DL>
+<HR>
+<A HREF="http://eol.ists.ca/cgi-bin/HyperNews/get/dunlop/pg95-user.html">HyperNews Forum</A> - About this Manual.
+<HR>
+<p align=center><B>POSTGRES95</B> is <A HREF="copy.html">copyright</A> © 1994-5 by the Regents of the
+University of California.<br><br>
+Converted to HTML by <a href="http://www.eol.ists.ca/~dunlop/dunlop.html">J. Douglas Dunlop</a>
+<a href="mailto:dunlop@eol.ists.ca"><dunlop@eol.ists.ca></a><br>
+The file
+<A HREF="http://www.eol.ists.ca/~dunlop/postgres95-manual/pg95user.tgz">
+pg95user.tgz</a> contains the complete manual for download.</p>
+</BODY>
+</HTML>
--- /dev/null
+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - THE QUERY LANGUAGE</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="start.html">[ Previous ]</A>
+<A HREF="advanced.html">[ Next ]</A>
+</font>
+<HR>
+<H1>4. THE QUERY LANGUAGE</H1>
+<HR>
+ The POSTGRES query language is a variant of <B>SQL-3</B>. It
+ has many extensions such as an extensible type system,
+ inheritance, functions and production rules. Those are
+ features carried over from the original POSTGRES query
+ language, POSTQUEL. This section provides an overview
+ of how to use POSTGRES <B>SQL</B> to perform simple operations.
+ This manual is only intended to give you an idea of our
+ flavor of <B>SQL</B> and is in no way a complete tutorial on
+ <B>SQL</B>. Numerous books have been written on <B>SQL</B>. For
+ instance, consult <A HREF="refs.html#MELT93">[MELT93]</A> or
+ <A HREF="refs.html#DATE93">[DATE93]</A>. You should also
+ be aware that some features are not part of the <B>ANSI</B>
+ standard.
+ In the examples that follow, we assume that you have
+ created the mydb database as described in the previous
+ subsection and have started <B>psql</B>.
+ Examples in this manual can also be found in
+ <CODE>/usr/local/postgres95/src/tutorial</CODE>. Refer to the
+ <CODE>README</CODE> file in that directory for how to use them. To
+ start the tutorial, do the following:
+<pre> % cd /usr/local/postgres95/src/tutorial
+ % psql -s mydb
+ Welcome to the POSTGRES95 interactive sql monitor:
+
+ type \? for help on slash commands
+ type \q to quit
+ type \g or terminate with semicolon to execute query
+ You are currently connected to the database: jolly
+
+
+ mydb=> \i basics.sql
+</pre>
+ The <B>\i</B> command read in queries from the specified
+ files. The <B>-s</B> option puts you in single step mode which
+ pauses before sending a query to the backend. Queries
+ in this section are in the file <CODE>basics.sql</CODE>.
+
+<H2><A NAME="concepts">4.1. Concepts</A></H2>
+ The fundamental notion in POSTGRES is that of a class,
+ which is a named collection of object instances. Each
+ instance has the same collection of named attributes,
+ and each attribute is of a specific type. Furthermore,
+ each instance has a permanent <B>object identifier (OID)</B>
+ that is unique throughout the installation. Because
+ <B>SQL</B> syntax refers to tables, we will <B>use the terms
+ table< and class interchangeably</B>. Likewise, a <B>row is an
+ instance</B> and <B>columns are attributes</B>.
+ As previously discussed, classes are grouped into
+ databases, and a collection of databases managed by a
+ single <B>postmaster</B> process constitutes an installation
+ or site.
+
+<H2><A NAME="creating-a-new-class">4.2. Creating a New Class</A></H2>
+ You can create a new class by specifying the class
+ name, along with all attribute names and their types:
+<pre> CREATE TABLE weather (
+ city varchar(80),
+ temp_lo int, -- low temperature
+ temp_hi int, -- high temperature
+ prcp real, -- precipitation
+ date date
+ );
+</pre>
+ Note that keywords are case-insensitive but identifiers
+ are case-sensitive. POSTGRES <B>SQL</B> supports the usual
+ <B>SQL</B> types <B>int, float, real, smallint, char(N),
+ varchar(N), date,</B> and <B>time</B>. As we will
+ see later, POSTGRES can be customized with an
+ arbitrary number of
+ user-defined data types. Consequently, type names are
+ not keywords.
+ So far, the POSTGRES create command looks exactly like
+ the command used to create a table in a traditional
+ relational system. However, we will presently see that
+ classes have properties that are extensions of the
+ relational model.
+
+<H2><A NAME="populating-a-class-with-instances">4.3. Populating a Class with Instances</A></H2>
+ The <B>insert</B> statement is used to populate a class with
+ instances:
+<pre> INSERT INTO weather
+ VALUES ('San Francisco', 46, 50, 0.25, '11/27/1994')
+</pre>
+ You can also use the <B>copy</B> command to perform load large
+ amounts of data from flat (<B>ASCII</B>) files.
+
+<H2><A NAME="querying-a-class">4.4. Querying a Class</A></H2>
+ The weather class can be queried with normal relational
+ selection and projection queries. A <B>SQL</B> <B>select</B>
+ statement is used to do this. The statement is divided into
+ a target list (the part that lists the attributes to be
+ returned) and a qualification (the part that specifies
+ any restrictions). For example, to retrieve all the
+ rows of weather, type:
+<pre> SELECT * FROM WEATHER;
+</pre>
+
+ and the output should be:
+<pre>
+ +--------------+---------+---------+------+------------+
+ |city | temp_lo | temp_hi | prcp | date |
+ +--------------+---------+---------+------+------------+
+ |San Francisco | 46 | 50 | 0.25 | 11-27-1994 |
+ +--------------+---------+---------+------+------------+
+ |San Francisco | 43 | 57 | 0 | 11-29-1994 |
+ +--------------+---------+---------+------+------------+
+ |Hayward | 37 | 54 | | 11-29-1994 |
+ +--------------+---------+---------+------+------------+
+</pre>
+ You may specify any aribitrary expressions in the target list. For example, you can do:
+<pre> * SELECT city, (temp_hi+temp_lo)/2 AS temp_avg, date FROM weather;
+</pre>
+ Arbitrary Boolean operators ( <B>and</B>, or and <B>not</B>) are
+ allowed in the qualification of any query. For example,
+<pre> SELECT *
+ FROM weather
+ WHERE city = 'San Francisco'
+ and prcp > 0.0;
+
+ +--------------+---------+---------+------+------------+
+ |city | temp_lo | temp_hi | prcp | date |
+ +--------------+---------+---------+------+------------+
+ |San Francisco | 46 | 50 | 0.25 | 11-27-1994 |
+ +--------------+---------+---------+------+------------+
+</pre>
+
+ As a final note, you can specify that the results of a
+ select can be returned in a <B>sorted order</B> or with <B>duplicate instances removed</B>.
+<pre> SELECT DISTINCT city
+ FROM weather
+ ORDER BY city;
+</pre>
+
+<H2><A NAME="redirecting-select-queries">4.5. Redirecting SELECT Queries</A></H2>
+ Any select query can be redirected to a new class
+<pre> SELECT * INTO temp from weather;
+</pre>
+ This creates an implicit create command, creating a new
+ class temp with the attribute names and types specified
+ in the target list of the <B>SELECT INTO</B> command. We can
+ then, of course, perform any operations on the resulting
+ class that we can perform on other classes.
+
+<H2><A NAME="joins-between-classes">4.6. Joins Between Classes</A></H2>
+ Thus far, our queries have only accessed one class at a
+ time. Queries can access multiple classes at once, or
+ access the same class in such a way that multiple
+ instances of the class are being processed at the same
+ time. A query that accesses multiple instances of the
+ same or different classes at one time is called a join
+ query.
+ As an example, say we wish to find all the records that
+ are in the temperature range of other records. In
+ effect, we need to compare the temp_lo and temp_hi
+ attributes of each EMP instance to the temp_lo and
+ temp_hi attributes of all other EMP instances.<A HREF="#2">2</A> We can
+ do this with the following query:
+<pre> SELECT W1.city, W1.temp_lo, W1.temp_hi,
+ W2.city, W2.temp_lo, W2.temp_hi
+ FROM weather W1, weather W2
+ WHERE W1.temp_lo < W2.temp_lo
+ and W1.temp_hi > W2.temp_hi;
+
+ +--------------+---------+---------+---------------+---------+---------+
+ |city | temp_lo | temp_hi | city | temp_lo | temp_hi |
+ +--------------+---------+---------+---------------+---------+---------+
+ |San Francisco | 43 | 57 | San Francisco | 46 | 50 |
+ +--------------+---------+---------+---------------+---------+---------+
+ |San Francisco | 37 | 54 | San Francisco | 46 | 50 |
+ +--------------+---------+---------+---------------+---------+---------+
+</pre>
+ In this case, both W1 and W2 are surrogates for an
+ instance of the class weather, and both range over all
+ instances of the class. (In the terminology of most
+ database systems, W1 and W2 are known as "range variables.")
+ A query can contain an arbitrary number of
+ class names and surrogates.<A HREF="#3">3</A>
+
+<H2><A NAME="updates">4.7. Updates</A></H2>
+ You can update existing instances using the update command.
+ Suppose you discover the temperature readings are
+ all off by 2 degrees as of Nov 28, you may update the
+ data as follow:
+<pre> * UPDATE weather
+ SET temp_hi = temp_hi - 2, temp_lo = temp_lo - 2
+ WHERE date > '11/28/1994;
+</pre>
+
+<H2><A NAME="deletions">4.8. Deletions</A></H2>
+ Deletions are performed using the <B>delete</B> command:
+<pre> * DELETE FROM weather WHERE city = 'Hayward';
+</pre>
+ All weather recording belongs to Hayward is removed.
+ One should be wary of queries of the form
+<pre> DELETE FROM classname;
+</pre>
+ Without a qualification, the delete command will simply
+ delete all instances of the given class, leaving it
+ empty. The system will not request confirmation before
+ doing this.
+
+<H2><A NAME="using-aggregate-functions">4.9. Using Aggregate Functions</A></H2>
+ Like most other query languages, POSTGRES supports
+ aggregate functions. However, the current
+ implementation of POSTGRES aggregate functions is very limited.
+ Specifically, while there are aggregates to compute
+ such functions as the <B>count, sum, average, maximum</B> and
+ <B>minimum</B> over a set of instances, aggregates can only
+ appear in the target list of a query and not in the
+ qualification ( where clause) As an example,
+<pre> SELECT max(temp_lo)
+ FROM weather;
+</pre>
+ Aggregates may also have <B>GROUP BY</B> clauses:
+<pre>
+ SELECT city, max(temp_lo)
+ FROM weather
+ GROUP BY city;
+</pre>
+<HR>
+ <A NAME="2"><B>2.</B></A> This is only a conceptual model. The actual join may
+ be performed in a more efficient manner, but this is invisible to the user.<br>
+
+ <A NAME="3"><B>3.</B></A> The semantics of such a join are
+ that the qualification
+ is a truth expression defined for the Cartesian product of
+ the classes indicated in the query. For those instances in
+ the Cartesian product for which the qualification is true,
+ POSTGRES computes and returns the values specified in the
+ target list. POSTGRES <B>SQL</B> does not assign any meaning to
+ duplicate values in such expressions. This means that POSTGRES
+ sometimes recomputes the same target list several times
+ this frequently happens when Boolean expressions are connected
+ with an or. To remove such duplicates, you must use
+ the select distinct statement.
+
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="start.html">[ Previous ]</A>
+<A HREF="advanced.html">[ Next ]</A>
+</font>
+</BODY>
+</HTML>
--- /dev/null
+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - REFERENCES</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="rules.html">[ Previous ]</A>
+<A HREF="appenda.html">[ Next ]</A>
+</font>
+<HR>
+<H1>16. REFERENCES</H1>
+<HR>
+<DL COMPACT>
+ <DT><A NAME="DATE93"><B>[DATE93]</B></A><DD>Date, C. J. and Darwen, Hugh, A Guide to The
+ SQL Standard, 3rd Edition, Reading, MA, June
+ 1993.
+ <DT><A NAME="MELT93"><B>[MELT93]</B></A><DD>Melton, J. Understanding the New SQL, 1994.
+ <DT><A NAME="ONG90"><B>[ONG90]</B></A><DD>Ong, L. and Goh, J., ``A Unified Framework
+ for Version Modeling Using Production Rules
+ in a Database System," Electronics Research
+ Laboratory, University of California, ERL
+ Technical Memorandum M90/33, Berkeley, CA,
+ April 1990.
+ <DT><A NAME="ROWE87"><B>[ROWE87]</B></A><DD>Rowe, L. and Stonebraker, M., ``The POSTGRES
+ Data Model,'' Proc. 1987 VLDB Conference,
+ Brighton, England, Sept. 1987.
+ <DT><A NAME="STON86"><B>[STON86]</B></A><DD>Stonebraker, M. and Rowe, L., ``The Design
+ of POSTGRES,'' Proc. 1986 ACM-SIGMOD Conference on Management of Data, Washington, DC,
+ May 1986.
+ <DT><A NAME="STON87a"><B>[STON87a]</B></A><DD>Stonebraker, M., Hanson, E. and Hong, C.-H.,
+ ``The Design of the POSTGRES Rules System,''
+ Proc. 1987 IEEE Conference on Data Engineering, Los Angeles, CA, Feb. 1987.
+ <DT><A NAME="STON87b"><B>[STON87b]</B></A><DD>Stonebraker, M., ``The POSTGRES Storage System,'' Proc. 1987 VLDB Conference, Brighton,
+ England, Sept. 1987.
+ <DT><A NAME="STON89"><B>[STON89]</B></A><DD>Stonebraker, M., Hearst, M., and Potamianos,
+ S., ``A Commentary on the POSTGRES Rules
+ System,'' SIGMOD Record 18(3), Sept. 1989.
+ <DT><A NAME="STON90a"><B>[STON90a]</B></A><DD>Stonebraker, M., Rowe, L. A., and Hirohama,
+ M., ``The Implementation of POSTGRES,'' IEEE
+ Transactions on Knowledge and Data Engineering 2(1), March 1990.
+ <DT><A NAME="STON90b"><B>[STON90b]</B></A><DD>Stonebraker, M. et al., ``On Rules, Procedures, Caching and Views in Database Systems,'' Proc. 1990 ACM-SIGMOD Conference on
+ Management of Data, Atlantic City, N.J.,
+ June 1990.
+</DL>
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
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+ <TITLE>The POSTGRES95 User Manual - THE POSTGRES RULE SYSTEM</TITLE>
+</HEAD>
+
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+
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+<HR>
+<H1>14. THE POSTGRES RULE SYSTEM
+</H1><HR>
+ Production rule systems are conceptually simple, but
+ there are many subtle points involved in actually using
+ them. Consequently, we will not attempt to explain the
+ actual syntax and operation of the POSTGRES rule system
+ here. Instead, you should read <A HREF="refs.html#STON90b">[STON90b]</A> to understand
+ some of these points and the theoretical foundations of
+ the POSTGRES rule system before trying to use rules.
+ The discussion in this section is intended to provide
+ an overview of the POSTGRES rule system and point the
+ user at helpful references and examples.
+ The "query rewrite" rule system modifies queries to
+ take rules into consideration, and then passes the modified
+ query to the query optimizer for execution. It
+ is very powerful, and can be used for many things such
+ as query language procedures, views, and versions. The
+ power of this rule system is discussed in
+ <A HREF="refs.html#ONG90">[ONG90]</A> as
+ well as <A HREF="refs.html#STON90b">[STON90b]</A>.
+<HR>
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+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - GETTING STARTED</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
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+<HR>
+<H1>3. GETTING STARTED WITH POSTGRES</H1>
+<HR>
+ This section discusses how to start POSTGRES and set up
+ your own environment so that you can use frontend
+ applications. We assume POSTGRES has already been
+ successfully installed. (Refer to the installation notes
+ for how to install POSTGRES.)
+<p>
+ Some of the steps listed in this section will apply to
+ all POSTGRES users, and some will apply primarily to
+ the site database administrator. This site administrator
+ is the person who installed the software, created
+ the database directories and started the <B>postmaster</B>
+ process. This person does not have to be the UNIX
+ superuser, "root," or the computer system administrator.
+ In this section, items for end users are labelled
+ "User" and items intended for the site administrator
+ are labelled "Admin."
+ Throughout this manual, any examples that begin with
+ the character ``%'' are commands that should be typed
+ at the UNIX shell prompt. Examples that begin with the
+ character ``*'' are commands in the POSTGRES query
+ language, POSTGRES <B>SQL</B>.
+
+<H2><A NAME="setting-up-your-environment">3.1. Admin/User: Setting Up Your Environment</A></H2>
+ <IMG SRC="figure02.gif" ALT="Figure 2. POSTGRES file layout.">
+ Figure 2. shows how the POSTGRES distribution is laid
+ out when installed in the default way. For simplicity,
+ we will assume that POSTGRES has been installed in the
+ directory /usr/local/postgres95. Therefore, wherever
+ you see the directory /usr/local/postgres95 you should
+ substitute the name of the directory where POSTGRES is
+ actually installed.
+ All POSTGRES commands are installed in the directory
+ /usr/local/postgres95/bin. Therefore, you should add
+ this directory to your shell command path. If you use
+ a variant of the Berkeley C shell, such as csh or tcsh,
+ you would add
+<pre> % set path = ( /usr/local/postgres95/bin $path )
+</pre>
+ in the .login file in your home directory. If you use
+ a variant of the Bourne shell, such as sh, ksh, or
+ bash, then you would add
+<pre>
+ % PATH=/usr/local/postgres95/bin:$PATH
+ % export PATH
+</pre>
+ to the .profile file in your home directory.
+ From now on, we will assume that you have added the
+ POSTGRES bin directory to your path. In addition, we
+ will make frequent reference to "setting a shell
+ variable" or "setting an environment variable" throughout
+ this document. If you did not fully understand the
+ last paragraph on modifying your search path, you
+ should consult the UNIX manual pages that describe your
+ shell before going any further.
+
+<H2><A NAME="starting-the-postmaster">3.2. Admin: Starting the <B>Postmaster</A></B></H2>
+ It should be clear from the preceding discussion that
+ nothing can happen to a database unless the <B>postmaster</B>
+ process is running. As the site administrator, there
+ are a number of things you should remember before
+ starting the <B>postmaster</B>. These are discussed in the
+ section of this manual titled, "Administering POSTGRES."
+ However, if POSTGRES has been installed by following
+ the installation instructions exactly as written, the
+ following simple command is all you should
+ need to start the <B>postmaster</B>:
+<pre> % postmaster &
+</pre>
+ The <B>postmaster</B> occasionally prints out messages which
+ are often helpful during troubleshooting. If you wish
+ to view debugging messages from the <B>postmaster</B>, you can
+ start it with the -d option and redirect the output to
+ the log file:
+<pre> % postmaster -d >& pm.log &
+</pre>
+ If you do not wish to see these messages, you can type
+<pre> % postmaster -S
+</pre>
+ and the <B>postmaster</B> will be "S"ilent. Notice that there
+ is no ampersand ("&") at the end of the last example.
+
+<H2><A NAME="adding-and-deleting-users">3.3. Admin: Adding and Deleting Users</A></H2>
+ The createuser command enables specific users to access
+ POSTGRES. The destroyuser command removes users and
+ prevents them from accessing POSTGRES. Note that these
+ commands only affect users with respect to POSTGRES;
+ they have no effect administration of users that the
+ operating system manages.
+
+<H2><A NAME="starting-applications">3.4. User: Starting Applications</A></H2>
+ Assuming that your site administrator has properly
+ started the <B>postmaster</B> process and authorized you to
+ use the database, you (as a user) may begin to start up
+ applications. As previously mentioned, you should add
+ /usr/local/postgres95/bin to your shell search path.
+ In most cases, this is all you should have to do in
+ terms of preparation.<A HREF="#1">1</A>
+ If you get the following error message from a POSTGRES
+ command (such as <B>psql</B> or createdb):
+<pre> connectDB() failed: Is the postmaster running at 'localhost' on port '4322'?
+</pre>
+ it is usually because (1) the <B>postmaster</B> is not running, or (2) you are attempting to connect to the wrong
+ server host.
+ If you get the following error message:
+<pre> FATAL 1:Feb 17 23:19:55:process userid (2360) !=
+ database owner (268)
+</pre>
+ it means that the site administrator started the <B>postmaster</B> as the wrong user. Tell him to restart it as
+ the POSTGRES superuser.
+
+<H2><A NAME="managing-a-database">3.5. User: Managing a Database</A></H2>
+ Now that POSTGRES is up and running we can create some
+ databases to experiment with. Here, we describe the
+ basic commands for managing a database.
+
+<H3><A NAME="creating-a-database">3.5.1. Creating a Database</A></H3>
+ Let's say you want to create a database named mydb.
+ You can do this with the following command:
+<pre> % createdb mydb
+</pre>
+
+ POSTGRES allows you to create any number of databases
+ at a given site and you automatically become the
+ database administrator of the database you just created. Database names must have an alphabetic first
+ character and are limited to 16 characters in length.
+ Not every user has authorization to become a database
+ administrator. If POSTGRES refuses to create databases
+ for you, then the site administrator needs to grant you
+ permission to create databases. Consult your site
+ administrator if this occurs.
+
+<H3><A NAME="accessing-a-database">3.5.2. Accessing a Database</A></H3>
+ Once you have constructed a database, you can access it
+ by:
+ <UL>
+ <LI>running the POSTGRES terminal monitor programs (
+ monitor or <B>psql</B>) which allows you to interactively
+ enter, edit, and execute <B>SQL</B> commands.
+ <LI>writing a C program using the LIBPQ subroutine
+ library. This allows you to submit <B>SQL</B> commands
+ from C and get answers and status messages back to
+ your program. This interface is discussed further
+ in section ??.
+ </UL>
+ You might want to start up <B>psql</B>, to try out the examples in this manual. It can be activated for the mydb
+ database by typing the command:
+<pre> % psql mydb
+</pre>
+ You will be greeted with the following message:
+<pre> Welcome to the POSTGRES95 interactive sql monitor:
+
+ type \? for help on slash commands
+ type \q to quit
+ type \g or terminate with semicolon to execute query
+ You are currently connected to the database: mydb
+
+ mydb=>
+</pre> This prompt indicates that the terminal monitor is listening to you and that you can type <B>SQL</B> queries into a
+ workspace maintained by the terminal monitor.
+ The <B>psql</B> program responds to escape codes that begin
+ with the backslash character, "\". For example, you
+ can get help on the syntax of various POSTGRES <B>SQL</B> commands by typing:
+<pre> mydb=> \h
+</pre>
+ Once you have finished entering your queries into the
+ workspace, you can pass the contents of the workspace
+ to the POSTGRES server by typing:
+<pre> mydb=> \g
+</pre>
+ This tells the server to process the query. If you
+ terminate your query with a semicolon, the \g is not
+ necessary. <B>psql</B> will automatically process semicolon terminated queries.
+ To read queries from a file, say myFile, instead of
+ entering them interactively, type:
+<pre> mydb=> \i fileName
+</pre>
+ To get out of <B>psql</B> and return to UNIX, type
+<pre> mydb=> \q
+</pre>
+ and <B>psql</B> will quit and return you to your command
+ shell. (For more escape codes, type \h at the monitor
+ prompt.)
+ White space (i.e., spaces, tabs and newlines) may be
+ used freely in <B>SQL</B> queries. Comments are denoted by
+ <b>--</b>. Everything after the dashes up to the end of the
+ line is ignored.
+
+<H3><A NAME="detroying-a-database">3.5.3. Destroying a Database</A></H3>
+ If you are the database administrator for the database
+ mydb, you can destroy it using the following UNIX command:
+<pre> % destroydb mydb
+</pre>
+ This action physically removes all of the UNIX files
+ associated with the database and cannot be undone, so
+ this should only be done with a great deal of fore-thought.
+
+<p>
+<HR>
+
+<A NAME="1"><B>1.</B></A> If your site administrator has not set things up in the
+default way, you may have some more work to do. For example, if the database server machine is a remote machine, you
+will need to set the <B>PGHOST</B> environment variable to the name
+of the database server machine. The environment variable
+<B>PGPORT</B> may also have to be set. The bottom line is this: if
+you try to start an application program and it complains
+that it cannot connect to the <B>postmaster</B>, you should immediately consult your site administrator to make sure that your
+environment is properly set up.
+
+<HR>
+<font size=-1>
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+ <TITLE>The POSTGRES95 User Manual - EXTENDING SQL: AGGREGATES</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
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+<A HREF="xoper.html">[ Previous ]</A>
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+</font>
+<HR>
+<H1>10. EXTENDING SQL: AGGREGATES</H1>
+<HR>
+ Aggregates in POSTGRES are expressed in terms of state
+ transition functions. That is, an aggregate can be
+ defined in terms of state that is modified whenever an
+ instance is processed. Some state functions look at a
+ particular value in the instance when computing the new
+ state (<B>sfunc1</B> in the create aggregate syntax) while
+ others only keep track of their own internal state
+ (<B>sfunc2</B>).
+ If we define an aggregate that uses only <B>sfunc1</B>, we
+ define an aggregate that computes a running function of
+ the attribute values from each instance. "Sum" is an
+ example of this kind of aggregate. "Sum" starts at
+ zero and always adds the current instance's value to
+ its running total. We will use the <B>int4pl</B> that is
+ built into POSTGRES to perform this addition.
+
+<pre> CREATE AGGREGATE complex_sum (
+ sfunc1 = complex_add,
+ basetype = complex,
+ stype1 = complex,
+ initcond1 = '(0,0)'
+ );
+
+
+ SELECT complex_sum(a) FROM test_complex;
+
+
+ +------------+
+ |complex_sum |
+ +------------+
+ |(34,53.9) |
+ +------------+
+</pre>
+
+ If we define only <B>sfunc2</B>, we are specifying an aggregate
+ that computes a running function that is independent of
+ the attribute values from each instance.
+ "Count" is the most common example of this kind of
+ aggregate. "Count" starts at zero and adds one to its
+ running total for each instance, ignoring the instance
+ value. Here, we use the built-in <B>int4inc</B> routine to do
+ the work for us. This routine increments (adds one to)
+ its argument.
+
+<pre> CREATE AGGREGATE my_count (sfunc2 = int4inc, -- add one
+ basetype = int4, stype2 = int4,
+ initcond2 = '0')
+
+ SELECT my_count(*) as emp_count from EMP;
+
+
+ +----------+
+ |emp_count |
+ +----------+
+ |5 |
+ +----------+
+</pre>
+
+ "Average" is an example of an aggregate that requires
+ both a function to compute the running sum and a function
+ to compute the running count. When all of the
+ instances have been processed, the final answer for the
+ aggregate is the running sum divided by the running
+ count. We use the <B>int4pl</B> and <B>int4inc</B> routines we used
+ before as well as the POSTGRES integer division
+ routine, <B>int4div</B>, to compute the division of the sum by
+ the count.
+
+<pre> CREATE AGGREGATE my_average (sfunc1 = int4pl, -- sum
+ basetype = int4,
+ stype1 = int4,
+ sfunc2 = int4inc, -- count
+ stype2 = int4,
+ finalfunc = int4div, -- division
+ initcond1 = '0',
+ initcond2 = '0')
+
+ SELECT my_average(salary) as emp_average FROM EMP;
+
+
+ +------------+
+ |emp_average |
+ +------------+
+ |1640 |
+ +------------+
+</pre>
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
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+ <TITLE>The POSTGRES95 User Manual - EXTENDING SQL: FUNCTIONS</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="extend.html">[ Previous ]</A>
+<A HREF="xtypes.html">[ Next ]</A>
+</font>
+<HR>
+<H1>7. EXTENDING <B>SQL</B>: FUNCTIONS</H1>
+<HR>
+ As it turns out, part of defining a new type is the
+ definition of functions that describe its behavior.
+ Consequently, while it is possible to define a new
+ function without defining a new type, the reverse is
+ not true. We therefore describe how to add new functions
+ to POSTGRES before describing how to add new
+ types.
+ POSTGRES <B>SQL</B> provides two types of functions: query
+ language functions (functions written in <B>SQL</B> and
+ programming language functions (functions written in a
+ compiled programming language such as <B>C</B>.) Either kind
+ of function can take a base type, a composite type or
+ some combination as arguments (parameters). In addition,
+ both kinds of functions can return a base type or
+ a composite type. It's easier to define <B>SQL</B> functions,
+ so we'll start with those.
+ Examples in this section can also be found in <CODE>funcs.sql</CODE>
+ and <CODE>C-code/funcs.c</CODE>.
+<p>
+<H2><A NAME="query-language-sql-functions">7.1. Query Language (<B>SQL</B>) Functions</A></H2>
+
+<H3><A NAME="sql-functions-on-base-types">7.1.1. <B>SQL</B> Functions on Base Types</A></H3>
+ The simplest possible <B>SQL</B> function has no arguments and
+ simply returns a base type, such as <B>int4</B>:
+
+<pre> CREATE FUNCTION one() RETURNS int4
+ AS 'SELECT 1 as RESULT' LANGUAGE 'sql';
+
+
+ SELECT one() AS answer;
+
+ +-------+
+ |answer |
+ +-------+
+ |1 |
+ +-------+
+</pre>
+ Notice that we defined a target list for the function
+ (with the name RESULT), but the target list of the
+ query that invoked the function overrode the function's
+ target list. Hence, the result is labelled answer
+ instead of one.
+<p>
+ It's almost as easy to define <B>SQL</B> functions that take
+ base types as arguments. In the example below, notice
+ how we refer to the arguments within the function as $1
+ and $2.
+
+<pre> CREATE FUNCTION add_em(int4, int4) RETURNS int4
+ AS 'SELECT $1 + $2;' LANGUAGE 'sql';
+
+
+ SELECT add_em(1, 2) AS answer;
+
+
+ +-------+
+ |answer |
+ +-------+
+ |3 |
+ +-------+
+</pre>
+
+<H3>7.1.2. <B>SQL</B> Functions on Composite Types</H3>
+ When specifying functions with arguments of composite
+ types (such as EMP), we must not only specify which
+ argument we want (as we did above with $1 and $2) but
+ also the attributes of that argument. For example,
+ take the function double_salary that computes what your
+ salary would be if it were doubled.
+
+<pre> CREATE FUNCTION double_salary(EMP) RETURNS int4
+ AS 'SELECT $1.salary * 2 AS salary;' LANGUAGE 'sql';
+
+ SELECT name, double_salary(EMP) AS dream
+ FROM EMP
+ WHERE EMP.dept = 'toy';
+
+
+ +-----+-------+
+ |name | dream |
+ +-----+-------+
+ |Sam | 2400 |
+ +-----+-------+
+</pre>
+ Notice the use of the syntax $1.salary.
+ Before launching into the subject of functions that
+ return composite types, we must first introduce the
+ function notation for projecting attributes. The simple way
+ to explain this is that we can usually use the
+ notation attribute(class) and class.attribute interchangably.
+
+<pre> --
+ -- this is the same as:
+ -- SELECT EMP.name AS youngster FROM EMP WHERE EMP.age < 30
+ --
+ SELECT name(EMP) AS youngster
+ FROM EMP
+ WHERE age(EMP) < 30;
+
+
+ +----------+
+ |youngster |
+ +----------+
+ |Sam |
+ +----------+
+</pre>
+ As we shall see, however, this is not always the case.
+ This function notation is important when we want to use
+ a function that returns a single instance. We do this
+ by assembling the entire instance within the function,
+ attribute by attribute. This is an example of a function
+ that returns a single EMP instance:
+
+<pre> CREATE FUNCTION new_emp() RETURNS EMP
+ AS 'SELECT \'None\'::text AS name,
+ 1000 AS salary,
+ 25 AS age,
+ \'none\'::char16 AS dept;'
+ LANGUAGE 'sql';
+</pre>
+
+ In this case we have specified each of the attributes
+ with a constant value, but any computation or expression
+ could have been substituted for these constants.
+ Defining a function like this can be tricky. Some of
+ the more important caveats are as follows:
+
+
+ <UL>
+ <LI>The target list order must be exactly the same as
+ that in which the attributes appear in the <B>CREATE
+ TABLE</B> statement (or when you execute a .* query).
+ <LI>You must be careful to typecast the expressions
+ (using ::) very carefully or you will see the following error:
+
+<pre> WARN::function declared to return type EMP does not retrieve (EMP.*)
+</pre>
+ <LI>When calling a function that returns an instance, we
+ cannot retrieve the entire instance. We must either
+ project an attribute out of the instance or pass the
+ entire instance into another function.
+<pre> SELECT name(new_emp()) AS nobody;
+
+
+ +-------+
+ |nobody |
+ +-------+
+ |None |
+ +-------+
+</pre>
+ <LI>The reason why, in general, we must use the function
+ syntax for projecting attributes of function return
+ values is that the parser just doesn't understand
+ the other (dot) syntax for projection when combined
+ with function calls.
+
+<pre> SELECT new_emp().name AS nobody;
+ WARN:parser: syntax error at or near "."
+</pre>
+ </UL>
+
+ Any collection of commands in the <B>SQL</B> query language
+ can be packaged together and defined as a function.
+ The commands can include updates (i.e., <B>insert</B>, <B>update</B>
+ and <B>delete</B>) as well as <B>select</B> queries. However, the
+ final command must be a <B>select</B> that returns whatever is
+ specified as the function's returntype.
+
+<pre>
+ CREATE FUNCTION clean_EMP () RETURNS int4
+ AS 'DELETE FROM EMP WHERE EMP.salary <= 0;
+ SELECT 1 AS ignore_this'
+ LANGUAGE 'sql';
+
+ SELECT clean_EMP();
+
+
+ +--+
+ |x |
+ +--+
+ |1 |
+ +--+
+</pre>
+<p>
+
+<H2><A NAME="programming-language-functions">7.2. Programming Language Functions</A></H2>
+<H3><A NAME="programming-language-functions-on-base-types">7.2.1. Programming Language Functions on Base Types</A></H3>
+ Internally, POSTGRES regards a base type as a "blob of
+ memory." The user-defined functions that you define
+ over a type in turn define the way that POSTGRES can
+ operate on it. That is, POSTGRES will only store and
+ retrieve the data from disk and use your user-defined
+ functions to input, process, and output the data.
+ Base types can have one of three internal formats:
+ <UL>
+ <LI>pass by value, fixed-length
+ <LI>pass by reference, fixed-length
+ <LI>pass by reference, variable-length
+ </UL>
+ By-value types can only be 1, 2 or 4 bytes in length
+ (even if your computer supports by-value types of other
+ sizes). POSTGRES itself only passes integer types by
+ value. You should be careful to define your types such
+ that they will be the same size (in bytes) on all
+ architectures. For example, the <B>long</B> type is dangerous
+ because it is 4 bytes on some machines and 8 bytes on
+ others, whereas <B>int</B> type is 4 bytes on most <B>UNIX</B>
+ machines (though not on most personal computers). A
+ reasonable implementation of the <B>int4</B> type on <B>UNIX</B>
+ machines might be:
+
+<pre> /* 4-byte integer, passed by value */
+ typedef int int4;
+</pre>
+
+ On the other hand, fixed-length types of any size may
+ be passed by-reference. For example, here is a sample
+ implementation of the POSTGRES char16 type:
+
+<pre> /* 16-byte structure, passed by reference */
+ typedef struct {
+ char data[16];
+ } char16;
+</pre>
+
+ Only pointers to such types can be used when passing
+ them in and out of POSTGRES functions.
+ Finally, all variable-length types must also be passed
+ by reference. All variable-length types must begin
+ with a length field of exactly 4 bytes, and all data to
+ be stored within that type must be located in the memory
+ immediately following that length field. The
+ length field is the total length of the structure
+ (i.e., it includes the size of the length field
+ itself). We can define the text type as follows:
+
+<pre> typedef struct {
+ int4 length;
+ char data[1];
+ } text;
+</pre>
+
+ Obviously, the data field is not long enough to hold
+ all possible strings -- it's impossible to declare such
+ a structure in <B>C</B>. When manipulating variable-length
+ types, we must be careful to allocate the correct
+ amount of memory and initialize the length field. For
+ example, if we wanted to store 40 bytes in a text
+ structure, we might use a code fragment like this:
+
+<pre> #include "postgres.h"
+ #include "utils/palloc.h"
+
+ ...
+
+ char buffer[40]; /* our source data */
+
+ ...
+
+ text *destination = (text *) palloc(VARHDRSZ + 40);
+ destination->length = VARHDRSZ + 40;
+ memmove(destination->data, buffer, 40);
+
+ ...
+
+</pre>
+ Now that we've gone over all of the possible structures
+ for base types, we can show some examples of real functions.
+ Suppose <CODE>funcs.c</CODE> look like:
+
+<pre> #include <string.h>
+ #include "postgres.h" /* for char16, etc. */
+ #include "utils/palloc.h" /* for palloc */
+
+ int
+ add_one(int arg)
+ {
+ return(arg + 1);
+ }
+
+ char16 *
+ concat16(char16 *arg1, char16 *arg2)
+ {
+ char16 *new_c16 = (char16 *) palloc(sizeof(char16));
+
+ memset((void *) new_c16, 0, sizeof(char16));
+ (void) strncpy(new_c16, arg1, 16);
+ return (char16 *)(strncat(new_c16, arg2, 16));
+ }
+<p>
+ text *
+ copytext(text *t)
+ {
+ /*
+ * VARSIZE is the total size of the struct in bytes.
+ */
+ text *new_t = (text *) palloc(VARSIZE(t));
+<p>
+ memset(new_t, 0, VARSIZE(t));
+<p>
+ VARSIZE(new_t) = VARSIZE(t);
+ /*
+ * VARDATA is a pointer to the data region of the struct.
+ */
+ memcpy((void *) VARDATA(new_t), /* destination */
+ (void *) VARDATA(t), /* source */
+ VARSIZE(t)-VARHDRSZ); /* how many bytes */
+<p>
+ return(new_t);
+ }
+</pre>
+ On <B>OSF/1</B> we would type:
+
+<pre> CREATE FUNCTION add_one(int4) RETURNS int4
+ AS '/usr/local/postgres95/tutorial/obj/funcs.so' LANGUAGE 'c';
+
+ CREATE FUNCTION concat16(char16, char16) RETURNS char16
+ AS '/usr/local/postgres95/tutorial/obj/funcs.so' LANGUAGE 'c';
+
+ CREATE FUNCTION copytext(text) RETURNS text
+ AS '/usr/local/postgres95/tutorial/obj/funcs.so' LANGUAGE 'c';
+</pre>
+
+ On other systems, we might have to make the filename
+ end in .sl (to indicate that it's a shared library).
+<p>
+<H3><A NAME="programming-language-functions-on-composite-types">7.2.2. Programming Language Functions on Composite Types</A></H3>
+ Composite types do not have a fixed layout like C
+ structures. Instances of a composite type may contain
+ null fields. In addition, composite types that are
+ part of an inheritance hierarchy may have different
+ fields than other members of the same inheritance hierarchy.
+ Therefore, POSTGRES provides a procedural
+ interface for accessing fields of composite types from
+ C.
+ As POSTGRES processes a set of instances, each instance
+ will be passed into your function as an opaque structure of type <B>TUPLE</B>.
+ Suppose we want to write a function to answer the query
+
+<pre> * SELECT name, c_overpaid(EMP, 1500) AS overpaid
+ FROM EMP
+ WHERE name = 'Bill' or name = 'Sam';
+</pre>
+ In the query above, we can define c_overpaid as:
+
+<pre> #include "postgres.h" /* for char16, etc. */
+ #include "libpq-fe.h" /* for TUPLE */
+<p>
+ bool
+ c_overpaid(TUPLE t,/* the current instance of EMP */
+ int4 limit)
+ {
+ bool isnull = false;
+ int4 salary;
+<p>
+ salary = (int4) GetAttributeByName(t, "salary", &isnull);
+<p>
+ if (isnull)
+ return (false);
+ return(salary > limit);
+ }
+</pre>
+
+ <B>GetAttributeByName</B> is the POSTGRES system function that
+ returns attributes out of the current instance. It has
+ three arguments: the argument of type TUPLE passed into
+ the function, the name of the desired attribute, and a
+ return parameter that describes whether the attribute
+ is null. <B>GetAttributeByName</B> will align data properly
+ so you can cast its return value to the desired type.
+ For example, if you have an attribute name which is of
+ the type char16, the <B>GetAttributeByName</B> call would look
+ like:
+
+<pre> char *str;
+ ...
+ str = (char *) GetAttributeByName(t, "name", &isnull)
+</pre>
+
+ The following query lets POSTGRES know about the
+ c_overpaid function:
+
+<pre> * CREATE FUNCTION c_overpaid(EMP, int4) RETURNS bool
+ AS '/usr/local/postgres95/tutorial/obj/funcs.so' LANGUAGE 'c';
+</pre>
+ While there are ways to construct new instances or modify
+ existing instances from within a C function, these
+ are far too complex to discuss in this manual.
+<p>
+<H3><A NAME="caveats">7.2.3. Caveats</A></H3>
+ We now turn to the more difficult task of writing
+ programming language functions. Be warned: this section
+ of the manual will not make you a programmer. You must
+ have a good understanding of <B>C</B> (including the use of
+ pointers and the malloc memory manager) before trying
+ to write <B>C</B> functions for use with POSTGRES.
+ While it may be possible to load functions written in
+ languages other than <B>C</B> into POSTGRES, this is often
+ difficult (when it is possible at all) because other
+ languages, such as <B>FORTRAN</B> and <B>Pascal</B> often do not follow
+ the same "calling convention" as <B>C</B>. That is, other
+ languages do not pass argument and return values
+ between functions in the same way. For this reason, we
+ will assume that your programming language functions
+ are written in <B>C</B>.
+ The basic rules for building <B>C</B> functions are as follows:
+ <OL>
+ <LI> Most of the header (include) files for POSTGRES
+ should already be installed in
+ /usr/local/postgres95/include (see Figure 2).
+ You should always include
+
+<pre> -I/usr/local/postgres95/include
+</pre>
+ on your cc command lines. Sometimes, you may
+ find that you require header files that are in
+ the server source itself (i.e., you need a file
+ we neglected to install in include). In those
+ cases you may need to add one or more of
+<pre>
+ -I/usr/local/postgres95/src/backend
+ -I/usr/local/postgres95/src/backend/include
+ -I/usr/local/postgres95/src/backend/port/<PORTNAME>
+ -I/usr/local/postgres95/src/backend/obj
+</pre>
+
+ (where <PORTNAME> is the name of the port, e.g.,
+ alpha or sparc).
+ <LI> When allocating memory, use the POSTGRES
+ routines palloc and pfree instead of the
+ corresponding <B>C</B> library routines malloc and free.
+ The memory allocated by palloc will be freed
+ automatically at the end of each transaction,
+ preventing memory leaks.
+ <LI> Always zero the bytes of your structures using
+ memset or bzero. Several routines (such as the
+ hash access method, hash join and the sort algorithm)
+ compute functions of the raw bits contained in
+ your structure. Even if you initialize all fields
+ of your structure, there may be
+ several bytes of alignment padding (holes in the
+ structure) that may contain garbage values.
+ <LI> Most of the internal POSTGRES types are declared
+ in postgres.h, so it's usually a good idea to
+ include that file as well.
+ <LI> Compiling and loading your object code so that
+ it can be dynamically loaded into POSTGRES
+ always requires special flags. See Appendix A
+ for a detailed explanation of how to do it for
+ your particular operating system.
+ </OL>
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
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+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - THE QUERY LANGUAGE</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
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+<HR>
+<H1>11. INTERFACING EXTENSIONS TO INDICES</H1>
+<HR>
+ The procedures described thus far let you define a new
+ type, new functions and new operators. However, we
+ cannot yet define a secondary index (such as a <B>B-tree</B>,
+ <B>R-tree</B> or hash access method) over a new type or its
+ operators.<p>
+
+ <A HREF="extend.html#about-the-postgres-system-catalogs">Look back at Figure 3</A>.
+ The right half shows the catalogs
+ that we must modify in order to tell POSTGRES how
+ to use a user-defined type and/or user-defined operators
+ with an index (i.e., <CODE>pg_am, pg_amop, pg_amproc</CODE> and
+ <CODE>pg_opclass</CODE>). Unfortunately, there is no simple command
+ to do this. We will demonstrate how to modify these
+ catalogs through a running example: a new operator
+ class for the <B>B-tree</B> access method that sorts integers
+ in ascending absolute value order.<p>
+
+ The <CODE>pg_am</CODE> class contains one instance for every user
+ defined access method. Support for the heap access
+ method is built into POSTGRES, but every other access
+ method is described here. The schema is
+<p>
+<center>
+<table border=1>
+<tr>
+ <td>amname </td><td> name of the access method </td>
+</tr>
+<td>amowner </td><td> object id of the owner's instance in pg_user </td>
+</tr>
+<tr>
+<td>amkind </td><td> not used at present, but set to 'o' as a place holder </td>
+</tr>
+<tr>
+<td>amstrategies </td><td> number of strategies for this access method (see below) </td>
+</tr>
+<tr>
+<td>amsupport </td><td> number of support routines for this access method (see below) </td>
+</tr>
+<tr>
+<td>amgettuple<br>
+ aminsert<br>
+ ...</td>
+<td>procedure identifiers for interface routines to the access
+ method. For example, regproc ids for opening, closing, and
+ getting instances from the access method appear here. </td>
+</tr>
+</table>
+</center>
+
+<p>
+
+ The <B>object ID</B> of the instance in <CODE>pg_am</CODE> is used as a
+ foreign key in lots of other classes. You don't need
+ to add a new instance to this class; all you're interested in
+ is the <B>object ID</B> of the access method instance
+ you want to extend:
+
+<pre> SELECT oid FROM pg_am WHERE amname = 'btree'
+
+ +----+
+ |oid |
+ +----+
+ |403 |
+ +----+
+</pre>
+
+ The <CODE>amstrategies</CODE> attribute exists to standardize
+ comparisons across data types. For example, <B>B-tree</B>s
+ impose a strict ordering on keys, lesser to greater.
+ Since POSTGRES allows the user to define operators,
+ POSTGRES cannot look at the name of an operator (eg, >
+ or <) and tell what kind of comparison it is. In fact,
+ some access methods don't impose any ordering at all.
+ For example, <B>R-tree</B>s express a rectangle-containment
+ relationship, whereas a hashed data structure expresses
+ only bitwise similarity based on the value of a hash
+ function. POSTGRES needs some consistent way of taking
+ a qualification in your query, looking at the operator
+ and then deciding if a usable index exists. This
+ implies that POSTGRES needs to know, for example, that
+ the <= and > operators partition a <B>B-tree</B>. POSTGRES
+ uses strategies to express these relationships between
+ operators and the way they can be used to scan indices.<p>
+
+ Defining a new set of strategies is beyond the scope of
+ this discussion, but we'll explain how <B>B-tree</B> strategies
+ work because you'll need to know that to add a new
+ operator class. In the <CODE>pg_am</CODE> class, the amstrategies
+ attribute is the number of strategies defined for this
+ access method. For <B>B-tree</B>s, this number is 5. These
+ strategies correspond to
+<p>
+
+<center>
+<table border=1>
+<tr>
+ <td>less than </td><td> 1 </td>
+</tr>
+<tr>
+ <td>less than or equal </td><td> 2 </td>
+</tr>
+<tr>
+ <td>equal </td><td> 3 </td>
+</tr>
+<tr>
+ <td>greater than or equal </td><td> 4 </td>
+</tr>
+<tr>
+ <td>greater than </td><td> 5 </td>
+</tr>
+</table>
+</center>
+<p>
+
+ The idea is that you'll need to add procedures corresponding
+ to the comparisons above to the <CODE>pg_amop</CODE> relation
+ (see below). The access method code can use these
+ strategy numbers, regardless of data type, to figure
+ out how to partition the <B>B-tree</B>, compute selectivity,
+ and so on. Don't worry about the details of adding
+ procedures yet; just understand that there must be a
+ set of these procedures for <CODE>int2, int4, oid,</CODE> and every
+ other data type on which a <B>B-tree</B> can operate.
+<p>
+ Sometimes, strategies aren't enough information for the
+ system to figure out how to use an index. Some access
+ methods require other support routines in order to
+ work. For example, the <B>B-tree</B> access method must be
+ able to compare two keys and determine whether one is
+ greater than, equal to, or less than the other.
+ Similarly, the <B>R-tree</B> access method must be able to compute
+ intersections, unions, and sizes of rectangles. These
+ operations do not correspond to user qualifications in
+ SQL queries; they are administrative routines used by
+ the access methods, internally.<p>
+
+ In order to manage diverse support routines
+ consistently across all POSTGRES access methods, <CODE>pg_am</CODE>
+ includes an attribute called <CODE>amsupport</CODE>. This attribute
+ records the number of support routines used by an
+ access method. For <B>B-tree</B>s, this number is one -- the
+ routine to take two keys and return -1, 0, or +1,
+ depending on whether the first key is less than, equal
+ to, or greater than the second.<A HREF="#8"><font size=-1>[8]</font></A><p>
+
+ The <CODE>amstrategies</CODE> entry in pg_am is just the number of
+ strategies defined for the access method in question.
+ The procedures for less than, less equal, and so on
+ don't appear in <CODE>pg_am</CODE>. Similarly, <CODE>amsupport</CODE> is just
+ the number of support routines required by the access
+ method. The actual routines are listed elsewhere.<p>
+
+ The next class of interest is pg_opclass. This class
+ exists only to associate a name with an oid. In
+ pg_amop, every <B>B-tree</B> operator class has a set of
+ procedures, one through five, above. Some existing
+ opclasses are <CODE>int2_ops, int4_ops, and oid_ops</CODE>. You
+ need to add an instance with your opclass name (for
+ example, <CODE>complex_abs_ops</CODE>) to <CODE>pg_opclass</CODE>. The <CODE>oid</CODE> of
+ this instance is a foreign key in other classes.
+
+<pre> INSERT INTO pg_opclass (opcname) VALUES ('complex_abs_ops');
+
+ SELECT oid, opcname
+ FROM pg_opclass
+ WHERE opcname = 'complex_abs_ops';
+
+ +------+--------------+
+ |oid | opcname |
+ +------+--------------+
+ |17314 | int4_abs_ops |
+ +------+--------------+
+</pre>
+
+ Note that the oid for your <CODE>pg_opclass</CODE> instance will be
+ different! You should substitute your value for 17314
+ wherever it appears in this discussion.<p>
+
+ So now we have an access method and an operator class.
+ We still need a set of operators; the procedure for
+ defining operators was discussed earlier in this manual.
+ For the complex_abs_ops operator class on Btrees,
+ the operators we require are:
+
+<pre> absolute value less-than
+ absolute value less-than-or-equal
+ absolute value equal
+ absolute value greater-than-or-equal
+ absolute value greater-than
+</pre>
+
+ Suppose the code that implements the functions defined
+ is stored in the file
+
+<pre>
+ /usr/local/postgres95/src/tutorial/complex.c
+</pre>
+
+ Part of the code look like this: (note that we will
+ only show the equality operator for the rest of the
+ examples. The other four operators are very similar.
+ Refer to <CODE>complex.c</CODE> or <CODE>complex.sql</CODE> for the details.)
+
+<pre> #define Mag(c) ((c)->x*(c)->x + (c)->y*(c)->y)
+
+ bool
+ complex_abs_eq(Complex *a, Complex *b)
+ {
+ double amag = Mag(a), bmag = Mag(b);
+ return (amag==bmag);
+ }
+</pre>
+
+ There are a couple of important things that are happening below.<p>
+
+ First, note that operators for less-than, less-than-or
+ equal, equal, greater-than-or-equal, and greater-than
+ for <CODE>int4</CODE> are being defined. All of these operators are
+ already defined for <CODE>int4</CODE> under the names <, <=, =, >=,
+ and >. The new operators behave differently, of
+ course. In order to guarantee that POSTGRES uses these
+ new operators rather than the old ones, they need to be
+ named differently from the old ones. This is a key
+ point: you can overload operators in POSTGRES, but only
+ if the operator isn't already defined for the argument
+ types. That is, if you have < defined for (int4,
+ int4), you can't define it again. POSTGRES does not
+ check this when you define your operator, so be careful.
+ To avoid this problem, odd names will be used for
+ the operators. If you get this wrong, the access methods
+ are likely to crash when you try to do scans.<p>
+
+ The other important point is that all the operator
+ functions return Boolean values. The access methods
+ rely on this fact. (On the other hand, the support
+ function returns whatever the particular access method
+ expects -- in this case, a signed integer.)
+ The final routine in the file is the "support routine"
+ mentioned when we discussed the amsupport attribute of
+ the <CODE>pg_am</CODE> class. We will use this later on. For now,
+ ignore it.
+
+<pre> CREATE FUNCTION complex_abs_eq(complex, complex)
+ RETURNS bool
+ AS '/usr/local/postgres95/tutorial/obj/complex.so'
+ LANGUAGE 'c';
+</pre>
+
+ Now define the operators that use them. As noted, the
+ operator names must be unique among all operators that
+ take two <CODE>int4</CODE> operands. In order to see if the
+ operator names listed below are taken, we can do a query on
+ <CODE>pg_operator</CODE>:
+
+<pre> /*
+ * this query uses the regular expression operator (~)
+ * to find three-character operator names that end in
+ * the character &
+ */
+ SELECT *
+ FROM pg_operator
+ WHERE oprname ~ '^..&$'::text;
+</pre>
+
+ to see if your name is taken for the types you want.
+ The important things here are the procedure (which are
+ the <B>C</B> functions defined above) and the restriction and
+ join selectivity functions. You should just use the
+ ones used below--note that there are different such
+ functions for the less-than, equal, and greater-than
+ cases. These must be supplied, or the access method
+ will crash when it tries to use the operator. You
+ should copy the names for restrict and join, but use
+ the procedure names you defined in the last step.
+
+<pre> CREATE OPERATOR = (
+ leftarg = complex, rightarg = complex, procedure = complex_abs_eq,
+ restrict = eqsel, join = eqjoinsel
+ )
+</pre>
+
+ Notice that five operators corresponding to less, less
+ equal, equal, greater, and greater equal are defined.<p>
+
+ We're just about finished. the last thing we need to do
+ is to update the <CODE>pg_amop</CODE> relation. To do this, we need
+ the following attributes:
+ <p>
+
+<center>
+<table border=1>
+ <td>amopid </td><td> the <CODE>oid</CODE> of the <CODE>pg_am</CODE> instance for B-tree
+ (== 403, see above) </td>
+<tr>
+</tr>
+ <td>amopclaid </td><td> the <CODE>oid</CODE> of the
+ <CODE>pg_opclass</CODE> instance for <CODE>int4_abs_ops</CODE> (==
+ whatever you got instead of <CODE>17314</CODE>, see above)</td>
+<tr>
+</tr>
+ <td>amopopr </td><td> the <CODE>oid</CODE>s of the operators for the opclass (which we'll
+ get in just a minute) </td>
+<tr>
+</tr>
+ <td>amopselect, amopnpages </td><td> cost functions.</td>
+</tr>
+</table>
+</center>
+<p>
+ The cost functions are used by the query optimizer to
+ decide whether or not to use a given index in a scan.
+ Fortunately, these already exist. The two functions
+ we'll use are <CODE>btreesel</CODE>, which estimates the selectivity
+ of the <B>B-tree</B>, and <CODE>btreenpage</CODE>, which estimates the
+ number of pages a search will touch in the tree.<p>
+
+ So we need the <CODE>oid</CODE>s of the operators we just defined.
+ We'll look up the names of all the operators that take
+ two <CODE>int4</CODE>s, and pick ours out:
+
+<pre> SELECT o.oid AS opoid, o.oprname
+ INTO TABLE complex_ops_tmp
+ FROM pg_operator o, pg_type t
+ WHERE o.oprleft = t.oid and o.oprright = t.oid
+ and t.typname = 'complex';
+
+ which returns:
+
+ +------+---------+
+ |oid | oprname |
+ +------+---------+
+ |17321 | < |
+ +------+---------+
+ |17322 | <= |
+ +------+---------+
+ |17323 | = |
+ +------+---------+
+ |17324 | >= |
+ +------+---------+
+ |17325 | > |
+ +------+---------+
+</pre>
+
+ (Again, some of your <CODE>oid</CODE> numbers will almost certainly
+ be different.) The operators we are interested in are
+ those with <CODE>oid</CODE>s 17321 through 17325. The values you
+ get will probably be different, and you should
+ substitute them for the values below. We can look at the
+ operator names and pick out the ones we just added.<p>
+
+ Now we're ready to update <CODE>pg_amop</CODE> with our new operator
+ class. The most important thing in this entire
+ discussion is that the operators are ordered, from less equal
+ through greater equal, in <CODE>pg_amop</CODE>. We add the
+ instances we need:
+
+<pre> INSERT INTO pg_amop (amopid, amopclaid, amopopr, amopstrategy,
+ amopselect, amopnpages)
+ SELECT am.oid, opcl.oid, c.opoid, 3,
+ 'btreesel'::regproc, 'btreenpage'::regproc
+ FROM pg_am am, pg_opclass opcl, complex_ops_tmp c
+ WHERE amname = 'btree' and opcname = 'complex_abs_ops'
+ and c.oprname = '=';
+</pre>
+
+ Note the order: "less than" is 1, "less than or equal"
+ is 2, "equal" is 3, "greater than or equal" is 4, and
+ "greater than" is 5.<p>
+
+ The last step (finally!) is registration of the
+ "support routine" previously described in our discussion of
+ <CODE>pg_am</CODE>. The <CODE>oid</CODE> of this support routine is stored in
+ the <CODE>pg_amproc</CODE> class, keyed by the access method <CODE>oid</CODE> and
+ the operator class <CODE>oid</CODE>. First, we need to register the
+ function in POSTGRES (recall that we put the <B>C</B> code
+ that implements this routine in the bottom of the file
+ in which we implemented the operator routines):
+
+<pre> CREATE FUNCTION int4_abs_cmp(int4, int4)
+ RETURNS int4
+ AS '/usr/local/postgres95/tutorial/obj/complex.so'
+ LANGUAGE 'c';
+
+ SELECT oid, proname FROM pg_proc WHERE prname = 'int4_abs_cmp';
+
+ +------+--------------+
+ |oid | proname |
+ +------+--------------+
+ |17328 | int4_abs_cmp |
+ +------+--------------+
+</pre>
+ (Again, your <CODE>oid</CODE> number will probably be different and
+ you should substitute the value you see for the value
+ below.) Recalling that the <B>B-tree</B> instance's oid is
+ 403 and that of <CODE>int4_abs_ops</CODE> is 17314, we can add the
+ new instance as follows:
+
+<pre> INSERT INTO pg_amproc (amid, amopclaid, amproc, amprocnum)
+ VALUES ('403'::oid, -- btree oid
+ '17314'::oid, -- pg_opclass tuple
+ '17328'::oid, -- new pg_proc oid
+ '1'::int2);
+</pre>
+<p>
+<HR>
+<A NAME="8"><B>[8]</B></A> Strictly speaking, this routine can return a negative
+number (< 0), 0, or a non-zero positive number (> 0).
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="xaggr.html">[ Previous ]</A>
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+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - THE QUERY LANGUAGE</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="xtypes.html">[ Previous ]</A>
+<A HREF="xaggr.html">[ Next ]</A>
+</font>
+<HR>
+<H1>9. EXTENDING SQL: OPERATORS</H1>
+<HR>
+ POSTGRES supports left unary, right unary and binary
+ operators. Operators can be overloaded, or re-used
+ with different numbers and types of arguments. If
+ there is an ambiguous situation and the system cannot
+ determine the correct operator to use, it will return
+ an error and you may have to typecast the left and/or
+ right operands to help it understand which operator you
+ meant to use.
+ To create an operator for adding two complex numbers
+ can be done as follows. First we need to create a
+ function to add the new types. Then, we can create the
+ operator with the function.
+
+<pre>
+ CREATE FUNCTION complex_add(complex, complex)
+ RETURNS complex
+ AS '$PWD/obj/complex.so'
+ LANGUAGE 'c';
+
+
+ CREATE OPERATOR + (
+ leftarg = complex,
+ rightarg = complex,
+ procedure = complex_add,
+ commutator = +
+ );
+</pre>
+
+ We've shown how to create a binary operator here. To
+ create unary operators, just omit one of leftarg (for
+ left unary) or rightarg (for right unary).
+ If we give the system enough type information, it can
+ automatically figure out which operators to use.
+
+<pre>
+ SELECT (a + b) AS c FROM test_complex;
+
+
+ +----------------+
+ |c |
+ +----------------+
+ |(5.2,6.05) |
+ +----------------+
+ |(133.42,144.95) |
+ +----------------+
+</pre>
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="xtypes.html">[ Previous ]</A>
+<A HREF="xaggr.html">[ Next ]</A>
+</font>
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+
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+<HTML>
+<HEAD>
+ <TITLE>The POSTGRES95 User Manual - EXTENDING SQL: TYPES</TITLE>
+</HEAD>
+
+<BODY>
+
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="xfunc.html">[ Previous ]</A>
+<A HREF="xoper.html">[ Next ]</A>
+</font>
+<HR>
+<H1>8. EXTENDING SQL: TYPES</H1>
+<HR>
+ As previously mentioned, there are two kinds of types
+ in POSTGRES: base types (defined in a programming language)
+ and composite types (instances).
+ Examples in this section up to interfacing indices can
+ be found in <CODE>complex.sql</CODE> and <CODE>complex.c</CODE>. Composite examples
+ are in <CODE>funcs.sql</CODE>.
+<p>
+<H2><A NAME="user-defined-types">8.1. User-Defined Types</A></H2>
+<p>
+<H3><A NAME="functions-needed-for-a-user-defined-type">8.1.1. Functions Needed for a User-Defined Type</A></H3>
+ A user-defined type must always have input and output
+ functions. These functions determine how the type
+ appears in strings (for input by the user and output to
+ the user) and how the type is organized in memory. The
+ input function takes a null-delimited character string
+ as its input and returns the internal (in memory)
+ representation of the type. The output function takes the
+ internal representation of the type and returns a null
+ delimited character string.
+ Suppose we want to define a complex type which represents
+ complex numbers. Naturally, we choose to represent a
+ complex in memory as the following <B>C</B> structure:
+
+<pre> typedef struct Complex {
+ double x;
+ double y;
+ } Complex;
+</pre>
+ and a string of the form (x,y) as the external string
+ representation.
+ These functions are usually not hard to write, especially
+ the output function. However, there are a number of points
+ to remember.
+
+ <OL>
+ <LI> When defining your external (string) representation,
+ remember that you must eventually write a
+ complete and robust parser for that representation
+ as your input function!
+
+<pre> Complex *
+ complex_in(char *str)
+ {
+ double x, y;
+ Complex *result;
+
+ if (sscanf(str, " ( %lf , %lf )", &x, &y) != 2) {
+ elog(WARN, "complex_in: error in parsing
+ return NULL;
+ }
+ result = (Complex *)palloc(sizeof(Complex));
+ result->x = x;
+ result->y = y;
+ return (result);
+ }
+</pre>
+
+ The output function can simply be:
+
+<pre> char *
+ complex_out(Complex *complex)
+ {
+ char *result;
+<p>
+ if (complex == NULL)
+ return(NULL);
+<p>
+ result = (char *) palloc(60);
+ sprintf(result, "(%g,%g)", complex->x, complex->y);
+ return(result);
+ }
+</pre>
+ <LI> You should try to make the input and output
+ functions inverses of each other. If you do
+ not, you will have severe problems when you need
+ to dump your data into a file and then read it
+ back in (say, into someone else's database on
+ another computer). This is a particularly common
+ problem when floating-point numbers are
+ involved.
+ </OL>
+ To define the <B>complex</B> type, we need to create the two
+ user-defined functions complex_in and complex_out
+ before creating the type:
+
+<pre> CREATE FUNCTION complex_in(opaque)
+ RETURNS complex
+ AS '/usr/local/postgres95/tutorial/obj/complex.so'
+ LANGUAGE 'c';
+
+ CREATE FUNCTION complex_out(opaque)
+ RETURNS opaque
+ AS '/usr/local/postgres95/tutorial/obj/complex.so'
+ LANGUAGE 'c';
+
+ CREATE TYPE complex (
+ internallength = 16,
+ input = complex_in,
+ output = complex_out
+ );
+</pre>
+
+ As discussed earlier, POSTGRES fully supports arrays of
+ base types. Additionally, POSTGRES supports arrays of
+ user-defined types as well. When you define a type,
+ POSTGRES automatically provides support for arrays of
+ that type. For historical reasons, the array type has
+ the same name as the user-defined type with the
+ underscore character _ prepended.
+ Composite types do not need any function defined on
+ them, since the system already understands what they
+ look like inside.
+<p>
+<H3><A NAME="large-objects">8.1.2. Large Objects</A></H3>
+ The types discussed to this point are all "small"
+ objects -- that is, they are smaller than 8KB<A HREF="#7"><font size=-1>[7]</font></A> in size.
+ If you require a larger type for something like a document
+ retrieval system or for storing bitmaps, you will
+ need to use the POSTGRES large object interface.
+<p>
+<HR>
+<A NAME="8"><B>[7]</B></A> 8 * 1024 == 8192 bytes. In fact, the type must be considerably smaller than 8192 bytes, since the POSTGRES tuple
+and page overhead must also fit into this 8KB limitation.
+The actual value that fits depends on the machine architecture.
+<HR>
+<font size=-1>
+<A HREF="pg95user.html">[ TOC ]</A>
+<A HREF="xfunc.html">[ Previous ]</A>
+<A HREF="xoper.html">[ Next ]</A>
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