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+$Header: /cvsroot/pgsql/doc/src/sgml/Attic/plsql.sgml,v 2.23 2001/03/17 01:53:22 thomas Exp $
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- <chapter id="plpgsql">
- <title>PL/pgSQL - <acronym>SQL</acronym> Procedural Language</title>
+<chapter id="plpgsql">
+ <title>PL/pgSQL - <acronym>SQL<acronym> Procedural Language</title>
- <para>
- PL/pgSQL is a loadable procedural language for the
- <productname>Postgres</productname> database system.
- </para>
-
- <para>
- This package was originally written by Jan Wieck.
- </para>
+ <para>
+ PL/pgSQL is a loadable procedural language for the
+ <productname>Postgres</productname> database system.
+ </para>
+
+ <para>
+ This package was originally written by Jan Wieck. This
+ documentation was re-organized and in part written
+ by Roberto Mello (rmello@fslc.usu.edu).
+ </para>
<sect1 id="plpgsql-overview">
<title>Overview</title>
<para>
For all expressions and <acronym>SQL</acronym> statements used in
the function, the PL/pgSQL bytecode interpreter creates a
- prepared execution plan using the <acronym>SPI</acronym> manager's <function>SPI_prepare()</function> and
- <function>SPI_saveplan()</function> functions. This is done the first time the individual
+ prepared execution plan using the <acronym>SPI</acronym> manager's
+ <function>SPI_prepare()</function> and
+ <function>SPI_saveplan()</function> functions. This is done the
+ first time the individual
statement is processed in the PL/pgSQL function. Thus, a function with
conditional code that contains many statements for which execution
plans would be required, will only prepare and save those plans
that are really used during the lifetime of the database
connection.
</para>
+ <para>
+ This means that you have to be careful about your user-defined
+ functions. For example:
+
+ <programlisting>
+CREATE FUNCTION populate() RETURNS INTEGER AS '
+DECLARE
+ -- Declarations
+BEGIN
+ PERFORM my_function();
+END;
+' language 'plpgsql';
+ </programlisting>
+ If you CREATE the above function, it will reference the ID for
+ my_function() in its bytecode. Later, if you DROP and re-CREATE
+ my_function(), populate() will not be able to find my_function()
+ anymore. You'll have to re-CREATE populate().
+ </para>
<para>
Because PL/pgSQL saves execution plans in this way, queries that appear
directly in a PL/pgSQL function must refer to the same tables and fields
create complex conditional computation functions and later use
them to define operators or use them in functional indices.
</para>
+ <sect2 id="plpgsql-advantages">
+ <title>Advantages of Using PL/pgSQL</title>
+
+ <itemizedlist>
+ <listitem>
+ <para>
+ <xref linkend="plpgsql-advantages-performance">Better performance</xref>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <xref linkend="plpgsql-advantages-sqlsupport">SQL Support</xref>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <xref linkend="plpgsql-advantages-portability">Portability</xref>
+ </para>
+ </listitem>
+ </itemizedlist>
+
+ <sect3 id="plpgsql-advantages-performance">
+ <title>Better Performance</title>
+ <para>
+ <acronym>SQL</acronym> is the language PostgreSQL (and
+ most other Relational Databases) use as query
+ language. It's portable and easy to learn. But every
+ <acronym>SQL</acronym> statement must be executed
+ individually by the database server.
+ </para>
+ <para>
+ That means that your client application must send each
+ query to the database server, wait for it to process it,
+ receive the results, do some computation, then send
+ other queries to the server. All this incurs inter
+ process communication and may also incur network
+ overhead if your client is on a different machine than
+ the database server.
+ </para>
+ <para>
+ With PL/pgSQL you can group a block of computation and a
+ series of queries <emphasis>inside</emphasis> the
+ database server, thus having the power of a procedural
+ language and the ease of use of SQL, but saving lots of
+ time because you don't have the whole client/server
+ communication overhead. Your application will enjoy a
+ considerable performance increase by using PL/pgSQL.
+ </para>
+ </sect3>
+ <sect3 id="plpgsql-advantages-sqlsupport">
+ <title>SQL Support</title>
+ <para>
+ PL/pgSQL adds the power of a procedural language to the
+ flexibility and ease of <acronym>SQL</acronym>. With
+ PL/pgSQL you can use all the datatypes, columns, operators
+ and functions of SQL.
+ </para>
+ </sect3>
+ <sect3 id="plpgsql-advantages-portability">
+ <title>Portability</title>
+ <para>
+ Because PL/pgSQL functions run inside PostgreSQL, these
+ functions will run on any platform where PostgreSQL
+ runs. Thus you can reuse code and have less development costs.
+ </para>
+ </sect3>
+ </sect2>
+
+ <sect2 id="plpgsql-overview-developing-in-plpgsql">
+ <title>Developing in PL/pgSQL</title>
+
+ <para>
+ Developing in PL/pgSQL is pretty straight forward, especially
+ if you have developed in other database procedural languages,
+ such as Oracle's PL/SQL. Two good ways of developing in
+ PL/pgSQL are:
+ <itemizedlist>
+ <listitem>
+ <para>
+ Using a text editor and reloading the file with <command>psql</command>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Using PostgreSQL's GUI Tool: pgaccess
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ One good way to develop in PL/pgSQL is to simply use the text
+ editor of your choice to create your functions, and in another
+ console, use <command>psql</command> (PostgreSQL's interactive monitor) to load
+ those functions. If you are doing it this way (and if you are
+ a PL/pgSQL novice or in debugging stage), it is a good idea to
+ always <command>DROP</command> your function before creating it. That way
+ when you reload the file, it'll drop your functions and then
+ re-create them. For example:
+ </para>
+ <para>
+ <programlisting>
+drop function testfunc(integer);
+create function testfunc(integer) return integer as '
+ ....
+end;
+' language 'plpgsql';
+ </programlisting>
+
+ When you load the file for the first time,
+ <productname>PostgreSQL</> will raise a warning saying this
+ function doesn't exist and go on to create it. To load an SQL
+ file (filename.sql) into a database named "dbname", use the command:
+ </para>
+ <para>
+ <programlisting>
+psql -f filename.sql dbname
+ </programlisting>
+
+ Another good way to develop in PL/pgSQL is using
+ <productname>PostgreSQL</>'s GUI tool: pgaccess. It does some
+ nice things for you, like escaping single-quotes, and making
+ it easy to recreate and debug functions.
+ </para>
+ </sect2>
</sect1>
<!-- **** PL/pgSQL Description **** -->
<title>Structure of PL/pgSQL</title>
<para>
- The PL/pgSQL language is case insensitive. All keywords and
- identifiers can be used in mixed upper- and lower-case.
- </para>
- <para>
- PL/pgSQL is a block oriented language. A block is defined as
+ PL/pgSQL is a <emphasis>block structured</emphasis>, case
+ insensitive language. All keywords and identifiers can be
+ used in mixed upper- and lower-case. A block is defined as:
+ </para>
-<synopsis>
+ <synopsis>
<optional><<label>></optional>
<optional>DECLARE
<replaceable>declarations</replaceable></optional>
BEGIN
<replaceable>statements</replaceable>
END;
-</synopsis>
- </para>
+ </synopsis>
<para>
There can be any number of sub-blocks in the statement section
of a block. Sub-blocks can be used to hide variables from outside a
- block of statements. The variables
- declared in the declarations section preceding a block are
- initialized to their default values every time the block is entered,
- not only once per function call.
+ block of statements.
+ </para>
+ <para>
+ The variables declared in the declarations section preceding a
+ block are initialized to their default values every time the
+ block is entered, not only once per function call. For example:
</para>
+ <programlisting>
+CREATE FUNCTION somefunc() RETURNS INTEGER AS '
+DECLARE
+ quantity INTEGER := 30;
+BEGIN
+ RAISE NOTICE ''Quantity here is %'',quantity; -- Quantity here is 30
+ quantity := 50;
+ --
+ -- Create a sub-block
+ --
+ DECLARE
+ quantity INTEGER := 80;
+ BEGIN
+ RAISE NOTICE ''Quantity here is %'',quantity; -- Quantity here is 80
+ END;
+
+ RAISE NOTICE ''Quantity here is %'',quantity; -- Quantity here is 50
+END;
+' language 'plpgsql';
+ </programlisting>
<para>
It is important not to confuse the use of BEGIN/END for
</para>
</sect2>
- <!-- **** PL/pgSQL declarations **** -->
-
+ <!-- **** PL/pgSQL Variables and Constants **** -->
<sect2>
- <title>Declarations</title>
+ <title>Variables and Constants</title>
<para>
All variables, rows and records used in a block or its
- sub-blocks must be declared in the declarations section of a block,
- except for the loop variable of a FOR-loop iterating over a range
- of integer values. Parameters given to a PL/pgSQL function are
- automatically declared with the usual identifiers <literal>$1</literal>, <literal>$2</literal>, etc.
- The declarations have the following syntax:
+ sub-blocks must be declared in the declarations section of a block.
+ The exception being the loop variable of a FOR loop iterating over a range
+ of integer values.
+ </para>
+ <para>
+ PL/pgSQL variables can have any SQL datatype, such as
+ <type>INTEGER</type>, <type>VARCHAR</type> and
+ <type>CHAR</type>. All variables have as default value the
+ <acronym>SQL</acronym> NULL value.
</para>
- <variablelist>
+ <para>
+ Here are some examples of variable declarations:
+ </para>
+ <programlisting>
+user_id INTEGER;
+quantity NUMBER(5);
+url VARCHAR;
+ </programlisting>
+
+ <sect3 id="plpgsql-description-default-vars">
+ <title>Constants and Variables With Default Values</title>
+
+ <para>
+ The declarations have the following syntax:
+ </para>
+ <synopsis>
+<replaceable>name</replaceable> <optional> CONSTANT </optional> <replaceable>type</replaceable> <optional> NOT NULL </optional> <optional> { DEFAULT | := } <replaceable>value</replaceable> </optional>;
+ </synopsis>
+ <para>
+ The value of variables declared as CONSTANT cannot be changed. If NOT NULL
+ is specified, an assignment of a NULL value results in a runtime
+ error. Since the default value of all variables is the
+ <acronym>SQL</acronym> NULL value, all variables declared as NOT NULL
+ must also have a default value specified.
+ </para>
+ <para>
+ The default value is evaluated every time the function is called. So
+ assigning '<literal>now</literal>' to a variable of type
+ <type>timestamp</type> causes the variable to have the
+ time of the actual function call, not when the function was
+ precompiled into its bytecode.
+ </para>
+ <para>
+ Examples:
+ </para>
+ <programlisting>
+quantity INTEGER := 32;
+url varchar := ''http://mysite.com'';
+user_id CONSTANT INTEGER := 10;
+ </programlisting>
+ </sect3>
+
+ <sect3 id="plpgsql-description-passed-vars">
+ <title>Variables Passed to Functions</title>
+
+ <para>
+ Variables passed to functions are named with the identifiers
+ <literal>$1</literal>, <literal>$2</literal>,
+ etc. (maximum is 16). Some examples:
+ </para>
+ <programlisting>
+CREATE FUNCTION sales_tax(REAL) RETURNS REAL AS '
+DECLARE
+ subtotal ALIAS FOR $1;
+BEGIN
+ return subtotal * 0.06;
+END;
+' language 'plpgsql';
- <varlistentry>
- <term>
-<replaceable>name</replaceable> <optional> CONSTANT </optional>
-<replaceable>type</replaceable> <optional> NOT NULL </optional> <optional> DEFAULT | :=
- <replaceable>value</replaceable> </optional>;
- </term>
- <listitem>
- <para>
- Declares a variable of the specified base type. If the variable
- is declared as CONSTANT, the value cannot be changed. If NOT NULL
- is specified, an assignment of a NULL value results in a runtime
- error. Since the default value of all variables is the
- <acronym>SQL</acronym> NULL value, all variables declared as NOT NULL
- must also have a default value specified.
- </para>
- <para>
- The default value is evaluated every time the block is entered. So
- assigning <literal>'now'</literal> to a variable of type
- <type>timestamp</type> causes the variable to have the
- time of the actual function call, not when the function was
- precompiled into its bytecode.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>
-<replaceable>name</replaceable> <replaceable>table</replaceable>%ROWTYPE;
- </term>
- <listitem>
- <para>
- Declares a row with the structure of the given table. <replaceable>table</replaceable> must be
- an existing table or view name of the database. The fields of the row
- are accessed in the dot notation. Parameters to a function can
- be composite types (complete table rows). In that case, the
- corresponding identifier $n will be a rowtype, but it
- must be aliased using the ALIAS command described below. Only the user
- attributes of a table row are accessible in the row, no Oid or other
- system attributes (because the row could be from a view and view rows
- don't have useful system attributes).
- </para>
- <para>
- The fields of the rowtype inherit the table's field sizes
- or precision for <type>char()</type> etc. data types.
- </para>
- </listitem>
- </varlistentry>
+CREATE FUNCTION instr(VARCHAR,INTEGER) RETURNS INTEGER AS '
+DECLARE
+ v_string ALIAS FOR $1;
+ index ALIAS FOR $2;
+BEGIN
+ -- Some computations here
+END;
+' language 'plpgsql';
+ </programlisting>
+ </sect3>
+
+ <sect3 id="plpgsql-description-attributes">
+ <title>Attributes</title>
+
+ <para>
+ Using the <type>%TYPE</type> and <type>%ROWTYPE</type>
+ attributes, you can declare variables with the same
+ datatype or structure of another database item (e.g: a
+ table field).
+ </para>
+
+ <variablelist>
+ <varlistentry>
+ <term>
+ %TYPE
+ </term>
+ <listitem>
+ <para>
+ <type>%TYPE</type> provides the datatype of a
+ variable or database column. You can use this to
+ declare variables that will hold database
+ values. For example, let's say you have a column
+ named <type>user_id</type> in your
+ <type>users</type> table. To declare a variable with
+ the same datatype as users you do:
+ </para>
+ <programlisting>
+user_id users.user_id%TYPE;
+ </programlisting>
+ <para>
+ By using <type>%TYPE</type> you don't need to know
+ the datatype of the structure you are referencing,
+ and most important, if the datatype of the
+ referenced item changes in the future (e.g: you
+ change your table definition of user_id to become a
+ REAL), you won't need to change your function
+ definition.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <replaceable>name</replaceable> <replaceable>table</replaceable>%ROWTYPE;
+ </term>
+ <listitem>
+ <para>
+ Declares a row with the structure of the given table. <replaceable>table</replaceable> must be
+ an existing table or view name of the database. The fields of the row
+ are accessed in the dot notation. Parameters to a function can
+ be composite types (complete table rows). In that case, the
+ corresponding identifier $n will be a rowtype, but it
+ must be aliased using the ALIAS command described above.
+ </para>
+
+ <para>
+ Only the user
+ attributes of a table row are accessible in the row, no OID or other
+ system attributes (because the row could be from a view).
+ The fields of the rowtype inherit the table's field sizes
+ or precision for <type>char()</type> etc. data types.
+ </para>
+ <programlisting>
+DECLARE
+ users_rec users%ROWTYPE;
+ user_id users%TYPE;
+BEGIN
+ user_id := users_rec.user_id;
+ ...
- <varlistentry>
- <term>
-<replaceable>name</replaceable> RECORD;
- </term>
- <listitem>
- <para>
- Records are similar to rowtypes, but they have no predefined structure.
- They are used in selections and FOR loops to hold one actual
- database row from a SELECT operation. One and the same record can be
- used in different selections. Accessing a record or an attempt to assign
- a value to a record field when there is no actual row in it results
- in a runtime error.
- </para>
- <para>
- The NEW and OLD rows in a trigger are given to the procedure as
- records. This is necessary because in <productname>Postgres</productname>
- one and the same trigger procedure can handle trigger events for
- different tables.
- </para>
- </listitem>
- </varlistentry>
+create function cs_refresh_one_mv(integer) returns integer as '
+ DECLARE
+ key ALIAS FOR $1;
+ table_data cs_materialized_views%ROWTYPE;
+ BEGIN
+ SELECT INTO table_data * FROM cs_materialized_views
+ WHERE sort_key=key;
+
+ IF NOT FOUND THEN
+ RAISE EXCEPTION ''View '' || key || '' not found'';
+ RETURN 0;
+ END IF;
- <varlistentry>
- <term>
-<replaceable>name</replaceable> ALIAS FOR $n;
- </term>
- <listitem>
- <para>
- For better readability of the code it is possible to define an alias
- for a positional parameter to a function.
- </para>
- <para>
- This aliasing is required for composite types given as arguments to
- a function. The dot notation $1.salary as in <acronym>SQL</acronym> functions is not
- allowed in PL/pgSQL.
- </para>
- </listitem>
- </varlistentry>
+ -- The mv_name column of cs_materialized_views stores view
+ -- names.
+
+ TRUNCATE TABLE table_data.mv_name;
+ INSERT INTO table_data.mv_name || '' '' || table_data.mv_query;
- <varlistentry>
- <term>
+ return 1;
+end;
+' language 'plpgsql';
+ </programlisting>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </sect3>
+
+ <sect3 id="plpgsql-description-remaning-vars">
+ <title>
+ RENAME
+ </title>
+ <para>
+ Using RENAME you can change the name of a variable, record
+ or row. This is useful if NEW or OLD should be referenced
+ by another name inside a trigger procedure.
+ </para>
+ <para>
+ Syntax and examples:
+ </para>
+ <programlisting>
RENAME <replaceable>oldname</replaceable> TO <replaceable>newname</replaceable>;
- </term>
- <listitem>
- <para>
- Change the name of a variable, record or row. This is useful
- if NEW or OLD should be referenced by another name inside a
- trigger procedure.
- </para>
- </listitem>
- </varlistentry>
-
- </variablelist>
- </sect2>
-
- <!-- **** PL/pgSQL data types **** -->
- <sect2>
- <title>Data Types</title>
-
- <para>
- The type of a variable can be any of the existing base types of
- the database. <replaceable>type</replaceable> in the declarations
- section above is defined as:
- </para>
- <para>
- <itemizedlist>
- <listitem>
- <para>
- <productname>Postgres</productname>-basetype
- </para>
- </listitem>
- <listitem>
- <para>
- <replaceable>variable</replaceable>%TYPE
- </para>
- </listitem>
- <listitem>
- <para>
- <replaceable>table.field</replaceable>%TYPE
- </para>
- </listitem>
- </itemizedlist>
- </para>
- <para>
- <replaceable>variable</replaceable> is the name of a variable,
- previously declared in the
- same function, that is visible at this point.
- </para>
- <para>
- <replaceable>table</replaceable> is the name of an existing table
- or view where <replaceable>field</replaceable> is the name of
- an attribute.
- </para>
- <para>
- Using the <replaceable>table.field</replaceable>%TYPE
- causes PL/pgSQL to look up the attributes definitions at the
- first call to the function during the lifetime of a backend.
- Suppose we have a table with a <type>char(20)</type> attribute and some PL/pgSQL functions
- that deal with its content in local variables. Now someone
- decides that <type>char(20)</type> is not enough, dumps the table, drops it,
- recreates it now with the attribute in question defined as
- <type>char(40)</type> and restores the data. Hah - he forgot about the
- functions. The computations inside them will truncate the values
- to 20 characters. But if they are defined using the
- <replaceable>table.field</replaceable>%TYPE
- declarations, they will automagically handle the size change or
- if the new table schema defines the attribute as <type>text</type> type.
- </para>
+RENAME id TO user_id;
+RENAME this_var TO that_var;
+ </programlisting>
+ </sect3>
</sect2>
<!-- **** PL/pgSQL expressions **** -->
<para>
All expressions used in PL/pgSQL statements are processed using
the backend's executor. Expressions that appear to contain
- constants may in fact require runtime evaluation (e.g., <literal>'now'</literal> for the
+ constants may in fact require run-time evaluation
+ (e.g. <literal>'now'</literal> for the
<type>timestamp</type> type) so
it is impossible for the PL/pgSQL parser
to identify real constant values other than the NULL keyword. All
expressions are evaluated internally by executing a query
-<synopsis>
+ <synopsis>
SELECT <replaceable>expression</replaceable>
-</synopsis>
+ </synopsis>
using the <acronym>SPI</acronym> manager. In the expression, occurrences of variable
identifiers are substituted by parameters and the actual values from
the variables are passed to the executor in the parameter array. All
The type checking done by the <productname>Postgres</productname>
main parser has some side
effects to the interpretation of constant values. In detail there
- is a difference between what the two functions
+ is a difference between what these two functions do:
-<programlisting>
CREATE FUNCTION logfunc1 (text) RETURNS timestamp AS '
DECLARE
logtxt ALIAS FOR $1;
RETURN ''now'';
END;
' LANGUAGE 'plpgsql';
-</programlisting>
+ </programlisting>
and
-<programlisting>
CREATE FUNCTION logfunc2 (text) RETURNS timestamp AS '
DECLARE
logtxt ALIAS FOR $1;
RETURN curtime;
END;
' LANGUAGE 'plpgsql';
-</programlisting>
-
- do. In the case of <function>logfunc1()</function>, the
- <productname>Postgres</productname> main parser knows when
- preparing the plan for the INSERT, that the string
- <literal>'now'</literal> should be interpreted as
- <type>timestamp</type> because the target field of logtable is of
- that type. Thus, it will make a constant from it at this time and
- this constant value is then used in all invocations of
+ </programlisting>
+
+ In the case of <function>logfunc1()</function>, the
+ <productname>Postgres</productname> main parser knows when
+ preparing the plan for the INSERT, that the string
+ <literal>'now'</literal> should be interpreted as
+ <type>timestamp</type> because the target field of logtable
+ is of that type. Thus, it will make a constant from it at this
+ time and this constant value is then used in all invocations of
<function>logfunc1()</function> during the lifetime of the
- backend. Needless to say that this isn't what the programmer
- wanted.
+ backend. Needless to say that this isn't what the
+ programmer wanted.
</para>
<para>
- In the case of <function>logfunc2()</function>, the <productname>Postgres</productname>
- main parser does not know
- what type <literal>'now'</literal> should become and therefore it returns a data type of
- <type>text</type> containing the string <literal>'now'</literal>. During the assignment
+ In the case of <function>logfunc2()</function>, the
+ <productname>Postgres</productname> main parser does not know
+ what type <literal>'now'</literal> should become and therefore
+ it returns a data type of <type>text</type> containing the string
+ <literal>'now'</literal>. During the assignment
to the local variable curtime, the PL/pgSQL interpreter casts this
- string to the timestamp type by calling the <function>text_out()</function> and <function>timestamp_in()</function>
+ string to the timestamp type by calling the
+ <function>text_out()</function> and <function>timestamp_in()</function>
functions for the conversion.
</para>
<para>
<!-- **** PL/pgSQL statements **** -->
- <sect2 id="plpgsql-statements">
- <title>Statements</title>
+ <sect2>
+ <title>Statements</title>
+ <para>
+ Anything not understood by the PL/pgSQL parser as specified below
+ will be put into a query and sent down to the database engine
+ to execute. The resulting query should not return any data.
+ </para>
+
+ <sect3 id="plpgsql-statements-assignment">
+ <title>Assignment</title>
<para>
- Anything not understood by the PL/pgSQL parser as specified below
- will be put into a query and sent down to the database engine
- to execute. The resulting query should not return any data.
- </para>
-
- <variablelist>
-
- <varlistentry>
- <term>Assignment</term>
- <listitem>
- <para>
- An assignment of a value to a variable or row/record field is
- written as
-<synopsis>
+ An assignment of a value to a variable or row/record field is
+ written as:
+ <synopsis>
<replaceable>identifier</replaceable> := <replaceable>expression</replaceable>;
-</synopsis>
- If the expressions result data type doesn't match the variables
- data type, or the variable has a size/precision that is known
- (as for <type>char(20)</type>), the result value will be implicitly cast by
- the PL/pgSQL bytecode interpreter using the result types output- and
- the variables type input-functions. Note that this could potentially
- result in runtime errors generated by the types input functions.
- </para>
- <para>
- An assignment of a complete selection into a record or row can
- be done by
-<synopsis>
-SELECT INTO <replaceable>target</replaceable> <replaceable>expressions</replaceable> FROM ...;
-</synopsis>
- <replaceable>target</replaceable> can be a record, a row variable or a
- comma separated list of variables and record-/row-fields. Note that
- this is quite different from Postgres' normal interpretation of
- SELECT INTO, which is that the INTO target is a newly created table.
- (If you want to create a table from a SELECT result inside a PL/pgSQL
- function, use the equivalent syntax CREATE TABLE AS SELECT.)
- </para>
- <para>
- if a row or a variable list is used as target, the selected values
- must exactly match the structure of the target(s) or a runtime error
- occurs. The FROM keyword can be followed by any valid qualification,
- grouping, sorting etc. that can be given for a SELECT statement.
- </para>
- <para>
- There is a special variable named FOUND of type <type>boolean</type> that can be used
- immediately after a SELECT INTO to check if an assignment had success.
+ </synopsis>
+
+ If the expressions result data type doesn't match the variables
+ data type, or the variable has a size/precision that is known
+ (as for <type>char(20)</type>), the result value will be implicitly casted by
+ the PL/pgSQL bytecode interpreter using the result types output- and
+ the variables type input-functions. Note that this could potentially
+ result in runtime errors generated by the types input functions.
+ </para>
-<programlisting>
-SELECT INTO myrec * FROM EMP WHERE empname = myname;
-IF NOT FOUND THEN
- RAISE EXCEPTION ''employee % not found'', myname;
-END IF;
-</programlisting>
+ <programlisting>
+user_id := 20;
+tax := subtotal * 0.06;
+ </programlisting>
+ </sect3>
- If the selection returns multiple rows, only the first is moved
- into the target fields. All others are silently discarded.
- </para>
- </listitem>
- </varlistentry>
+ <sect3 id="plpgsql-statements-calling-other-funcs">
+ <title>Calling another function</title>
- <varlistentry>
- <term>Calling another function</term>
- <listitem>
- <para>
- All functions defined in a <productname>Postgres</productname>
- database return a value. Thus, the normal way to call a function
- is to execute a SELECT query or doing an assignment (resulting
- in a PL/pgSQL internal SELECT). But there are cases where someone
- is not interested in the function's result.
-<synopsis>
+ <para>
+ All functions defined in a <productname>Postgres</productname>
+ database return a value. Thus, the normal way to call a function
+ is to execute a SELECT query or doing an assignment (resulting
+ in a PL/pgSQL internal SELECT).
+ </para>
+ <para>
+ But there are cases where someone is not interested in the
+ function's result. In these cases, use the PERFORM
+ statement.
+ </para>
+ <synopsis>
PERFORM <replaceable>query</replaceable>
-</synopsis>
- executes a <literal>SELECT <replaceable>query</replaceable></literal> over the
- <acronym>SPI</acronym> manager and discards the result. Identifiers like local
- variables are still substituted into parameters.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>Executing dynamic queries</term>
- <listitem>
- <para>
-<synopsis>
+ </synopsis>
+ <para>
+ executes a <literal>SELECT <replaceable>query</replaceable></literal> over the
+ <acronym>SPI manager</acronym> and discards the result. Identifiers like local
+ variables are still substituted into parameters.
+ </para>
+ <programlisting>
+PERFORM create_mv(''cs_session_page_requests_mv'',''
+ select session_id, page_id, count(*) as n_hits,
+ sum(dwell_time) as dwell_time, count(dwell_time) as dwell_count
+ from cs_fact_table
+ group by session_id, page_id '');
+ </programlisting>
+ </sect3>
+
+ <sect3 id="plpgsql-statements-executing-dyn-queries">
+ <title>Executing dynamic queries</title>
+
+ <para>
+ Often times you will want to generate dynamic queries inside
+ your PL/pgSQL functions. Or you have functions that will
+ generate other functions. PL/pgSQL provides the EXECUTE
+ statement for these occasions.
+ </para>
+ <para>
+ <synopsis>
EXECUTE <replaceable class="command">query-string</replaceable>
-</synopsis>
- where <replaceable>query-string</replaceable> is a string of
- type <type>text</type> containing the <replaceable>query</replaceable> to be
- executed.
+ </synopsis>
+ where <replaceable>query-string</replaceable> is a string of
+ type <type>text</type> containing the <replaceable>query</replaceable> to be
+ executed.
</para>
-
+ <para>
+ When working with dynamic queries you will have to face
+ escaping of single quotes in PL/pgSQL. Please refer to the
+ table available at the "Porting from Oracle PL/SQL" chapter
+ for a detailed explanation that will save you some effort.
+ </para>
+
<para>
Unlike all other queries in PL/pgSQL, a
<replaceable>query</replaceable> run by an EXECUTE statement
within the procedure to perform actions on variable tables and
fields.
</para>
-
+
<para>
- The results from SELECT queries are discarded by EXECUTE, and
- SELECT INTO is not currently supported within EXECUTE. So, the
- only way to extract a result from a dynamically-created SELECT
- is to use the FOR ... EXECUTE form described later.
+ The results from SELECT queries are discarded by EXECUTE, and
+ SELECT INTO is not currently supported within EXECUTE. So, the
+ only way to extract a result from a dynamically-created SELECT
+ is to use the FOR ... EXECUTE form described later.
</para>
<para>
An example:
-<programlisting>
+ <synopsis>
EXECUTE ''UPDATE tbl SET ''
|| quote_ident(fieldname)
|| '' = ''
|| quote_literal(newvalue)
|| '' WHERE ...'';
-</programlisting>
- This example shows use of the functions
- <function>quote_ident</function>(<type>TEXT</type>) and
- <function>quote_literal</function>(<type>TEXT</type>).
- Variables containing field and table identifiers should be
- passed to function <function>quote_ident()</function>.
- Variables containing literal elements of the dynamic query
- string should be passed to
- <function>quote_literal()</function>. Both take the
- appropriate steps to return the input text enclosed in single
- or double quotes and with any embedded special characters
- properly escaped.
+ </synopsis>
+ </para>
+ <para>
+ This example shows use of the functions
+ <function>quote_ident</function>(<type>TEXT</type>) and
+ <function>quote_literal</function>(<type>TEXT</type>).
+ Variables containing field and table identifiers should be
+ passed to function <function>quote_ident()</function>.
+ Variables containing literal elements of the dynamic query
+ string should be passed to
+ <function>quote_literal()</function>. Both take the
+ appropriate steps to return the input text enclosed in single
+ or double quotes and with any embedded special characters.
</para>
- </listitem>
- </varlistentry>
+ <para>
+ Here is a much larger example of a dynamic query and EXECUTE:
+ <programlisting>
+CREATE FUNCTION cs_update_referrer_type_proc() RETURNS INTEGER AS '
+DECLARE
+ referrer_keys RECORD; -- Declare a generic record to be used in a FOR
+ a_output varchar(4000);
+BEGIN
+ a_output := ''CREATE FUNCTION cs_find_referrer_type(varchar,varchar,varchar)
+ RETURNS varchar AS ''''
+ DECLARE
+ v_host ALIAS FOR $1;
+ v_domain ALIAS FOR $2;
+ v_url ALIAS FOR $3; '';
- <varlistentry>
- <term>Obtaining other results status</term>
- <listitem>
- <para>
-<synopsis>
-GET DIAGNOSTICS <replaceable>variable</replaceable> = <replaceable>item</replaceable> <optional> , ... </optional>
-</synopsis>
- This command allows retrieval of system status indicators. Each
- <replaceable>item</replaceable> is a keyword identifying a state
- value to be assigned to the specified variable (which should be of
- the right datatype to receive it). The currently available status
- items are <varname>ROW_COUNT</>, the number of rows processed by
- the last <acronym>SQL</acronym> query sent down to the <acronym>SQL</acronym> engine; and
- <varname>RESULT_OID</>, the Oid of the last row inserted by the
- most recent <acronym>SQL</acronym> query. Note that <varname>RESULT_OID</> is only
- useful after an INSERT query.
- </para>
- </listitem>
- </varlistentry>
+ --
+ -- Notice how we scan through the results of a query in a FOR loop
+ -- using the FOR <record> construct.
+ --
- <varlistentry>
- <term>Returning from the function</term>
- <listitem>
- <para>
-<synopsis>
-RETURN <replaceable>expression</replaceable>
-</synopsis>
- The function terminates and the value of <replaceable>expression</replaceable>
- will be returned to the upper executor. The return value of a function
- cannot be undefined. If control reaches the end of the top-level block
- of the function without hitting a RETURN statement, a runtime error
- will occur.
- </para>
- <para>
- The expressions result will be automatically casted into the
- function's return type as described for assignments.
- </para>
- </listitem>
- </varlistentry>
+ FOR referrer_keys IN select * from cs_referrer_keys order by try_order LOOP
+ a_output := a_output || '' if v_'' || referrer_keys.kind || '' like ''''''''''
+ || referrer_keys.key_string || '''''''''' then return ''''''
+ || referrer_keys.referrer_type || ''''''; end if;'';
+ END LOOP;
+
+ a_output := a_output || '' return null; end; '''' language ''''plpgsql'''';'';
+
+ -- This works because we are not substituting any variables
+ -- Otherwise it would fail. Look at PERFORM for another way to run functions
+
+ EXECUTE a_output;
+end;
+' language 'plpgsql';
+ </programlisting>
+ </para>
+ </sect3>
- <varlistentry>
- <term>Aborting and messages</term>
- <listitem>
+ <sect3 id="plpgsql-statements-diagnostics">
+ <title>Obtaining other results status</title>
<para>
- As indicated in the above examples there is a RAISE statement that
- can throw messages into the <productname>Postgres</productname>
- elog mechanism.
-<synopsis>
-RAISE <replaceable class="parameter">level</replaceable> '<replaceable class="parameter">format</replaceable>' <optional>, <replaceable class="parameter">identifier</replaceable> <optional>...</optional></optional>;
-</synopsis>
- Inside the format, <literal>%</literal> is used as a placeholder for the
- subsequent comma-separated identifiers. Possible levels are
- DEBUG (silently suppressed in production running databases), NOTICE
- (written into the database log and forwarded to the client application)
- and EXCEPTION (written into the database log and aborting the transaction).
+ <synopsis>
+GET DIAGNOSTICS <replaceable>variable</replaceable> = <replaceable>item</replaceable> <optional> , ... </optional>
+ </synopsis>
+ This command allows retrieval of system status indicators. Each
+ <replaceable>item</replaceable> is a keyword identifying a state
+ value to be assigned to the specified variable (which should be of
+ the right datatype to receive it). The currently available status
+ items are <varname>ROW_COUNT</>, the number of rows processed by
+ the last <acronym>SQL</acronym> query sent down to the <acronym>SQL</acronym> engine; and
+ <varname>RESULT_OID</>, the Oid of the last row inserted by the
+ most recent <acronym>SQL</acronym> query. Note that <varname>RESULT_OID</> is only
+ useful after an INSERT query.
</para>
- </listitem>
- </varlistentry>
+ </sect3>
+
+ <sect3 id="plpgsql-statements-returning">
+ <title>Returning from a function</title>
- <varlistentry>
- <term>Conditionals</term>
- <listitem>
- <para>
-<synopsis>
-IF <replaceable>expression</replaceable> THEN
- <replaceable>statements</replaceable>
-<optional>ELSE
- <replaceable>statements</replaceable></optional>
-END IF;
-</synopsis>
- The <replaceable>expression</replaceable> must return a value that
- is of type <type>boolean</type> or can be casted to a <type>boolean</type>.
+ <para>
+ <synopsis>
+RETURN <replaceable>expression</replaceable>
+ </synopsis>
+ The function terminates and the value of <replaceable>expression</replaceable>
+ will be returned to the upper executor. The return value of a function
+ cannot be undefined. If control reaches the end of the top-level block
+ of the function without hitting a RETURN statement, a runtime error
+ will occur.
</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
-Loops
- </term>
- <listitem>
<para>
- There are multiple types of loops.
-<synopsis>
-<optional><<label>></optional>
-LOOP
- <replaceable>statements</replaceable>
-END LOOP;
-</synopsis>
- An unconditional loop that must be terminated explicitly
- by an EXIT statement. The optional label can be used by
- EXIT statements of nested loops to specify which level of
- nesting should be terminated.
-<synopsis>
-<optional><<label>></optional>
-WHILE <replaceable>expression</replaceable> LOOP
- <replaceable>statements</replaceable>
-END LOOP;
-</synopsis>
- A conditional loop that is executed as long as the evaluation
- of <replaceable>expression</replaceable> is true.
-<synopsis>
-<optional><<label>></optional>
-FOR <replaceable>name</replaceable> IN <optional> REVERSE </optional> <replaceable>expression</replaceable> .. <replaceable>expression</replaceable> LOOP
- <replaceable>statements</replaceable>
-END LOOP;
-</synopsis>
- A loop that iterates over a range of integer values. The variable
- <replaceable>name</replaceable> is automatically created as type
- integer and exists only inside the loop. The two expressions giving
- the lower and upper bound of the range are evaluated only when entering
- the loop. The iteration step is always 1.
-<synopsis>
-<optional><<label>></optional>
-FOR <replaceable>record | row</replaceable> IN <replaceable>select_clause</replaceable> LOOP
- <replaceable>statements</replaceable>
-END LOOP;
-</synopsis>
- The record or row is assigned all the rows resulting from the select
- clause and the loop body is executed for each row. If the loop is
- terminated with an EXIT statement, the last assigned row is still
- accessible after the loop.
-<synopsis>
-<optional><<label>></optional>
-FOR <replaceable>record | row</replaceable> IN EXECUTE <replaceable>text_expression</replaceable> LOOP
- <replaceable>statements</replaceable>
-END LOOP;
-</synopsis>
- This is like the previous form, except that the source SELECT
- statement is specified as a string expression, which is evaluated
- and re-planned on each entry to the FOR loop. This allows the
- programmer to choose the speed of a pre-planned query or the
- flexibility of a dynamic query, just as with a plain EXECUTE
- statement.
-<synopsis>
-EXIT <optional> <replaceable>label</replaceable> </optional> <optional> WHEN <replaceable>expression</replaceable> </optional>;
-</synopsis>
- If no <replaceable>label</replaceable> given,
- the innermost loop is terminated and the
- statement following END LOOP is executed next.
- If <replaceable>label</replaceable> is given, it
- must be the label of the current or an upper level of nested loop
- blocks. Then the named loop or block is terminated and control
- continues with the statement after the loops/blocks corresponding
- END.
+ The expressions result will be automatically casted into the
+ function's return type as described for assignments.
</para>
- </listitem>
- </varlistentry>
-
- </variablelist>
+ </sect3>
+ </sect2>
- </sect2>
+ <!-- **** PL/pgSQL Control Structures **** -->
- <!-- **** PL/pgSQL trigger procedures **** -->
+ <sect2 id="plpgsql-description-control-structures">
- <sect2>
- <title>Trigger Procedures</title>
+ <title>Control Structures</title>
+ <para>
+ Control structures are probably the most useful (and
+ important) part of PL/SQL. With PL/pgSQL's control structures,
+ you can manipulate <productname>PostgreSQL</> data in a very
+ flexible and powerful way.
+ </para>
+
+ <sect3 id="plpgsql-description-control-structures-conditionals">
+ <title>Conditional Control: IF statements</title>
<para>
- PL/pgSQL can be used to define trigger procedures. They are created
- with the usual CREATE FUNCTION command as a function with no
- arguments and a return type of OPAQUE.
- </para>
- <para>
- There are some <productname>Postgres</productname> specific details
- in functions used as trigger procedures.
- </para>
- <para>
- First they have some special variables created automatically in the
- top-level blocks declaration section. They are
+ <function>IF</function> statements let you take action
+ according to certain conditions. PL/pgSQL has three forms of
+ IF: IF-THEN, IF-THEN-ELSE, IF-THEN-ELSE IF. NOTE: All
+ PL/pgSQL IF statements need a corresponding <function>END
+ IF</function> statement. In ELSE-IF statements you need two:
+ one for the first IF and one for the second (ELSE IF).
</para>
<variablelist>
<varlistentry>
- <term><varname>NEW</varname></term>
+ <term>
+ IF-THEN
+ </term>
<listitem>
<para>
- Data type RECORD; variable holding the new database row on INSERT/UPDATE
- operations on ROW level triggers.
+ IF-THEN statements is the simplest form of an IF. The
+ statements between THEN and END IF will be executed if
+ the condition is true. Otherwise, the statements
+ following END IF will be executed.
+ <programlisting>
+IF v_user_id <> 0 THEN
+ UPDATE users SET email = v_email WHERE user_id = v_user_id;
+END IF;
+ </programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><varname>OLD</varname></term>
+ <term>
+ IF-THEN-ELSE
+ </term>
<listitem>
<para>
- Data type RECORD; variable holding the old database row on UPDATE/DELETE
- operations on ROW level triggers.
- </para>
- </listitem>
- </varlistentry>
+ IF-THEN-ELSE statements adds to IF-THEN by letting you
+ specify the statements that should be executed if the
+ condition evaluates to FALSE.
+ <programlisting>
+IF parentid IS NULL or parentid = ''''
+THEN
+ return fullname;
+ELSE
+ return hp_true_filename(parentid) || ''/'' || fullname;
+END IF;
- <varlistentry>
- <term><varname>TG_NAME</varname></term>
- <listitem>
+
+IF v_count > 0 THEN
+ INSERT INTO users_count(count) VALUES(v_count);
+ return ''t'';
+ELSE
+ return ''f'';
+END IF;
+ </programlisting>
+ </para>
<para>
- Data type <type>name</type>; variable that contains the name of the trigger actually
- fired.
+ IF statements can be nested and in the following
+ example:
+ <programlisting>
+IF demo_row.sex = ''m'' THEN
+ pretty_sex := ''man'';
+ELSE
+ IF demo_row.sex = ''f'' THEN
+ pretty_sex := ''woman'';
+ END IF;
+END IF;
+ </programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><varname>TG_WHEN</varname></term>
+ <term>
+ IF-THEN-ELSE IF
+ </term>
<listitem>
<para>
- Data type <type>text</type>; a string of either <literal>'BEFORE'</literal> or <literal>'AFTER'</literal> depending on the
- triggers definition.
+ When you use the "ELSE IF" statement, you are actually
+ nesting an IF statement inside the ELSE
+ statement. Thus you need one END IF statement for each
+ nested IF and one for the parent IF-ELSE.
</para>
+ <para>
+ For example:
+ <programlisting>
+IF demo_row.sex = ''m'' THEN
+ pretty_sex := ''man'';
+ELSE IF demo_row.sex = ''f'' THEN
+ pretty_sex := ''woman'';
+ END IF;
+END IF;
+ </programlisting>
+ </para>
</listitem>
</varlistentry>
+ </variablelist>
+ </sect3>
+ <sect3 id="plpgsql-description-control-structures-loops">
+ <title>Iterative Control: LOOP, WHILE, FOR and EXIT</title>
+
+ <para>
+ With the LOOP, WHILE, FOR and EXIT statements, you can
+ control the flow of execution of your PL/pgSQL program
+ iteratively.
+ </para>
+ <variablelist>
<varlistentry>
- <term><varname>TG_LEVEL</varname></term>
+ <term>
+ LOOP
+ </term>
<listitem>
<para>
- Data type <type>text</type>; a string of either <literal>'ROW'</literal> or <literal>'STATEMENT'</literal> depending on the
- triggers definition.
+ <synopsis>
+<optional><<label>></optional>
+LOOP
+ <replaceable>statements</replaceable>
+END LOOP;
+ </synopsis>
+ An unconditional loop that must be terminated explicitly
+ by an EXIT statement. The optional label can be used by
+ EXIT statements of nested loops to specify which level of
+ nesting should be terminated.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><varname>TG_OP</varname></term>
+ <term>
+ EXIT
+ </term>
<listitem>
<para>
- Data type <type>text</type>; a string of <literal>'INSERT'</literal>, <literal>'UPDATE'</literal>, or <literal>'DELETE'</literal> telling
- for which operation the trigger is actually fired.
+ <synopsis>
+EXIT <optional> <replaceable>label</replaceable> </optional> <optional> WHEN <replaceable>expression</replaceable> </optional>;
+ </synopsis>
+ If no <replaceable>label</replaceable> is given,
+ the innermost loop is terminated and the
+ statement following END LOOP is executed next.
+ If <replaceable>label</replaceable> is given, it
+ must be the label of the current or an upper level of nested loop
+ blocks. Then the named loop or block is terminated and control
+ continues with the statement after the loops/blocks corresponding
+ END.
</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><varname>TG_RELID</varname></term>
- <listitem>
<para>
- Data type oid; the object ID of the table that caused the
- trigger invocation.
+ Examples:
+ <programlisting>
+LOOP
+ -- some computations
+ IF count > 0 THEN
+ EXIT; -- exit loop
+ END IF;
+END LOOP;
+
+LOOP
+ -- some computations
+ EXIT WHEN count > 0;
+END LOOP;
+
+BEGIN
+ -- some computations
+ IF stocks > 100000 THEN
+ EXIT; -- illegal. Can't use EXIT outside of a LOOP
+ END IF;
+END;
+ </programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><varname>TG_RELNAME</varname></term>
+ <term>
+ WHILE
+ </term>
<listitem>
<para>
- Data type name; the name of the table that caused the trigger
- invocation.
+ With the WHILE statement, you can loop through a
+ sequence of statements as long as the evaluation of
+ the condition expression is true.
</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><varname>TG_NARGS</varname></term>
- <listitem>
<para>
- Data type integer; the number of arguments given to the trigger
- procedure in the CREATE TRIGGER statement.
+ <synopsis>
+<optional><<label>></optional>
+WHILE <replaceable>expression</replaceable> LOOP
+ <replaceable>statements</replaceable>
+END LOOP;
+ </synopsis>
+ <para>
+ For example:
+ </para>
+ <programlisting>
+WHILE amount_owed > 0 AND gift_certificate_balance > 0 LOOP
+ -- some computations here
+END LOOP;
+
+WHILE NOT boolean_expression LOOP
+ -- some computations here
+END LOOP;
+ </programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><varname>TG_ARGV[]</varname></term>
+ <term>
+ FOR
+ </term>
<listitem>
<para>
- Data type array of <type>text</type>; the arguments from the CREATE TRIGGER statement.
- The index counts from 0 and can be given as an expression. Invalid
- indices (< 0 or >= tg_nargs) result in a NULL value.
+ <synopsis>
+<optional><<label>></optional>
+FOR <replaceable>name</replaceable> IN <optional> REVERSE </optional> <replaceable>expression</replaceable> .. <replaceable>expression</replaceable> LOOP
+ <replaceable>statements</replaceable>
+END LOOP;
+ </synopsis>
+ A loop that iterates over a range of integer values. The variable
+ <replaceable>name</replaceable> is automatically created as type
+ integer and exists only inside the loop. The two expressions giving
+ the lower and upper bound of the range are evaluated only when entering
+ the loop. The iteration step is always 1.
+ </para>
+ <para>
+ Some examples of FOR loops (see <xref linkend="plpgsql-description-records"></xref> for
+ iterating over records in FOR loops):
+ <programlisting>
+FOR i IN 1..10 LOOP
+ -- some expressions here
+
+ RAISE NOTICE 'i is %',i;
+END LOOP;
+
+FOR i IN REVERSE 1..10 LOOP
+ -- some expressions here
+END LOOP;
+ </programlisting>
</para>
</listitem>
</varlistentry>
</variablelist>
+ </sect3>
+ </sect2>
+ <!-- **** PL/pgSQL records **** -->
+
+ <sect2 id="plpgsql-description-records">
+ <title>Working with RECORDs</title>
+ <para>
+ Records are similar to rowtypes, but they have no predefined structure.
+ They are used in selections and FOR loops to hold one actual
+ database row from a SELECT operation.
+ </para>
+
+ <sect3 id="plpgsql-description-records-declaration">
+ <title>Declaration</title>
<para>
- Second they must return either NULL or a record/row containing
- exactly the structure of the table the trigger was fired for.
- Triggers fired AFTER might always return a NULL value with no
- effect. Triggers fired BEFORE signal the trigger manager
- to skip the operation for this actual row when returning NULL.
- Otherwise, the returned record/row replaces the inserted/updated
- row in the operation. It is possible to replace single values directly
- in NEW and return that or to build a complete new record/row to
- return.
+ One variables of type RECORD can be used for different
+ selections. Accessing a record or an attempt to assign
+ a value to a record field when there is no actual row in it results
+ in a runtime error. They can be declared like this:
</para>
- </sect2>
+ <para>
+ <synopsis>
+<replaceable>name</replaceable> RECORD;
+ </synopsis>
+ </para>
+ </sect3>
+ <sect3 id="plpgsql-description-records-assignment">
+ <title>Assignments</title>
+ <para>
+ An assignment of a complete selection into a record or row can
+ be done by:
+ <synopsis>
+SELECT INTO <replaceable>target</replaceable> <replaceable>expressions</replaceable> FROM ...;
+ </synopsis>
+ <replaceable>target</replaceable> can be a record, a row variable or a
+ comma separated list of variables and record-/row-fields. Note that
+ this is quite different from Postgres' normal interpretation of
+ SELECT INTO, which is that the INTO target is a newly created table.
+ (If you want to create a table from a SELECT result inside a PL/pgSQL
+ function, use the equivalent syntax <command>CREATE TABLE AS SELECT</command>.)
+ </para>
+ <para>
+ If a row or a variable list is used as target, the selected values
+ must exactly match the structure of the target(s) or a runtime error
+ occurs. The FROM keyword can be followed by any valid qualification,
+ grouping, sorting etc. that can be given for a SELECT statement.
+ </para>
+ <para>
+ Once a record or row has been assigned to a RECORD variable,
+ you can use the "." (dot) notation to access fields in that
+ record:
+ </para>
+ <para>
+ <programlisting>
+DECLARE
+ users_rec RECORD;
+ full_name varchar;
+BEGIN
+ SELECT INTO users_rec * FROM users WHERE user_id=3;
+
+ full_name := users_rec.first_name || '' '' || users_rec.last_name;
+ </programlisting>
+ </para>
+ <para>
+ There is a special variable named FOUND of type <type>boolean</type> that can be used
+ immediately after a SELECT INTO to check if an assignment had success.
+
+ <programlisting>
+SELECT INTO myrec * FROM EMP WHERE empname = myname;
+IF NOT FOUND THEN
+ RAISE EXCEPTION ''employee % not found'', myname;
+END IF;
+ </programlisting>
+
+ You can also use the IS NULL (or ISNULL) conditionals to
+ test for NULLity of a RECORD/ROW. If the selection returns
+ multiple rows, only the first is moved into the target
+ fields. All others are silently discarded.
+ </para>
+ <para>
+ <programlisting>
+DECLARE
+ users_rec RECORD;
+ full_name varchar;
+BEGIN
+ SELECT INTO users_rec * FROM users WHERE user_id=3;
+
+ IF users_rec.homepage IS NULL THEN
+ -- user entered no homepage, return "http://"
+
+ return ''http://'';
+ END IF;
+END;
+ </programlisting>
+ </para>
+ </sect3>
+ <sect3 id="plpgsql-description-records-iterating">
+ <title>Iterating Through Records</title>
+
+ <para>
+ Using a special type of FOR loop, you can iterate through
+ the results of a query and manipulate that data
+ accordingly. The syntax is as follow:
+ </para>
+ <para>
+ <synopsis>
+<optional><<label>></optional>
+FOR <replaceable>record | row</replaceable> IN <replaceable>select_clause</replaceable> LOOP
+ <replaceable>statements</replaceable>
+END LOOP;
+ </synopsis>
+ The record or row is assigned all the rows
+ resulting from the select clause and the loop body executed
+ for each. Here is an example:
+ </para>
+ <para>
+ <programlisting>
+create function cs_refresh_mviews () returns integer as '
+DECLARE
+ mviews RECORD;
+
+ -- Instead, if you did:
+ -- mviews cs_materialized_views%ROWTYPE;
+ -- this record would ONLY be usable for the cs_materialized_views table
+
+BEGIN
+ PERFORM cs_log(''Refreshing materialized views...'');
+
+ FOR mviews IN SELECT * FROM cs_materialized_views ORDER BY sort_key LOOP
+
+ -- Now "mviews" has one record from cs_materialized_views
+
+ PERFORM cs_log(''Refreshing materialized view '' || mview.mv_name || ''...'');
+ TRUNCATE TABLE mview.mv_name;
+ INSERT INTO mview.mv_name || '' '' || mview.mv_query;
+ END LOOP;
+
+ PERFORM cs_log(''Done refreshing materialized views.'');
+ return 1;
+end;
+' language 'plpgsql';
+ </programlisting>
+
+ If the loop is terminated with an EXIT statement,
+ the last assigned row is still accessible after the loop.
+ </para>
+ <para>
+ The FOR-IN EXECUTE statement is another way to iterate over
+ records:
+ </para>
+ <para>
+ <synopsis>
+<optional><<label>></optional>
+FOR <replaceable>record | row</replaceable> IN EXECUTE <replaceable>text_expression</replaceable> LOOP
+ <replaceable>statements</replaceable>
+END LOOP;
+ </synopsis>
+ This is like the previous form, except that the source SELECT
+ statement is specified as a string expression, which is evaluated
+ and re-planned on each entry to the FOR loop. This allows the
+ programmer to choose the speed of a pre-planned query or the
+ flexibility of a dynamic query, just as with a plain EXECUTE
+ statement.
+ </para>
+ </sect3>
+ </sect2>
+
+ <sect2 id="plpgsql-description-aborting-and-messages">
+ <title>Aborting and Messages</title>
+
+ <para>
+ Use the RAISE statement to throw messages into the
+ <productname>Postgres</productname> elog mechanism.
+
+ <synopsis>
+RAISE <replaceable class="parameter">level</replaceable> '<replaceable class="parameter">format</replaceable>' <optional>, <replaceable class="parameter">identifier</replaceable> <optional>...</optional></optional>;
+ </synopsis>
+ Inside the format, <literal>%</literal> is used as a placeholder for the
+ subsequent comma-separated identifiers. Possible levels are
+ DEBUG (silently suppressed in production running databases), NOTICE
+ (written into the database log and forwarded to the client application)
+ and EXCEPTION (written into the database log and aborting the transaction).
+ </para>
+ <para>
+ <programlisting>
+RAISE NOTICE ''Id number '' || key || '' not found!'';
+RAISE NOTICE ''Calling cs_create_job(%)'',v_job_id;
+ </programlisting>
+ In this last example, v_job_id will replace the % in the
+ string.
+ </para>
+ <para>
+ <programlisting>
+RAISE EXCEPTION ''Inexistent ID --> %'',user_id;
+ </programlisting>
+ This will abort the transaction and write to the database log.
+ </para>
+ </sect2>
<!-- **** PL/pgSQL exceptions **** -->
statement) this happened.
</para>
</sect2>
- </sect1>
+ </sect1>
- <!-- **** PL/pgSQL Examples **** -->
- <sect1 id="plpgsql-examples">
- <title>Examples</title>
+ <!-- **** PL/pgSQL trigger procedures **** -->
+
+ <sect1 id="plpgsql-trigger">
+ <title>Trigger Procedures</title>
+ <sect2 id="plpgsql-trigger-description">
+ <title>Description</title>
<para>
- Here are only a few functions to demonstrate how easy it is to write PL/pgSQL
- functions. For more complex examples the programmer
- might look at the regression test for PL/pgSQL.
+ PL/pgSQL can be used to define trigger procedures. They are created
+ with the usual <command>CREATE FUNCTION</command> command as a function with no
+ arguments and a return type of <type>OPAQUE</type>.
</para>
-
<para>
- One painful detail in writing functions in PL/pgSQL is the handling
- of single quotes. The function's source text in the <command>CREATE FUNCTION</command> command must
- be a literal string. Single quotes inside of literal strings must be
- either doubled or quoted with a backslash. We are still looking for
- an elegant alternative. In the meantime, doubling the single quotes
- as in the examples below should be used. Any solution for this
- in future versions of <productname>Postgres</productname> will be
- forward compatible.
+ There are some <productname>Postgres</productname> specific details
+ in functions used as trigger procedures.
</para>
+ <para>
+ First they have some special variables created automatically in the
+ top-level blocks declaration section. They are
+ </para>
+
+ <variablelist>
+ <varlistentry>
+ <term><varname>NEW</varname></term>
+ <listitem>
+ <para>
+ Data type <type>RECORD</type>; variable holding the new database row on INSERT/UPDATE
+ operations on ROW level triggers.
+ </para>
+ </listitem>
+ </varlistentry>
- <example>
- <title>A Simple PL/pgSQL Functions</title>
+ <varlistentry>
+ <term><varname>OLD</varname></term>
+ <listitem>
+ <para>
+ Data type <type>RECORD</type>; variable holding the old database row on UPDATE/DELETE
+ operations on ROW level triggers.
+ </para>
+ </listitem>
+ </varlistentry>
- <para>
- The following two PL/pgSQL functions are identical to their
- counterparts from the C language function discussion.
+ <varlistentry>
+ <term><varname>TG_NAME</varname></term>
+ <listitem>
+ <para>
+ Data type <type>name</type>; variable that contains the name of the trigger actually
+ fired.
+ </para>
+ </listitem>
+ </varlistentry>
-<programlisting>
-CREATE FUNCTION add_one (integer) RETURNS integer AS '
- BEGIN
- RETURN $1 + 1;
- END;
-' LANGUAGE 'plpgsql';
-</programlisting>
+ <varlistentry>
+ <term><varname>TG_WHEN</varname></term>
+ <listitem>
+ <para>
+ Data type <type>text</type>; a string of either
+ <literal>BEFORE</literal> or <literal>AFTER</literal>
+ depending on the triggers definition.
+ </para>
+ </listitem>
+ </varlistentry>
-<programlisting>
-CREATE FUNCTION concat_text (text, text) RETURNS text AS '
- BEGIN
- RETURN $1 || $2;
- END;
-' LANGUAGE 'plpgsql';
-</programlisting>
- </para>
+ <varlistentry>
+ <term><varname>TG_LEVEL</varname></term>
+ <listitem>
+ <para>
+ Data type <type>text</type>; a string of either
+ <literal>ROW</literal> or <literal>STATEMENT</literal> depending on the
+ triggers definition.
+ </para>
+ </listitem>
+ </varlistentry>
- </example>
+ <varlistentry>
+ <term><varname>TG_OP</varname></term>
+ <listitem>
+ <para>
+ Data type <type>text</type>; a string of
+ <literal>INSERT</literal>, <literal>UPDATE</literal>
+ or <literal>DELETE</literal> telling
+ for which operation the trigger is actually fired.
+ </para>
+ </listitem>
+ </varlistentry>
- <example>
- <title>A PL/pgSQL Function on a Composite Type</title>
+ <varlistentry>
+ <term><varname>TG_RELID</varname></term>
+ <listitem>
+ <para>
+ Data type <type>oid</type>; the object ID of the table that caused the
+ trigger invocation.
+ </para>
+ </listitem>
+ </varlistentry>
- <para>
- Again, this is the PL/pgSQL equivalent to the example from
- the C functions.
+ <varlistentry>
+ <term><varname>TG_RELNAME</varname></term>
+ <listitem>
+ <para>
+ Data type <type>name</type>; the name of the table that caused the trigger
+ invocation.
+ </para>
+ </listitem>
+ </varlistentry>
-<programlisting>
-CREATE FUNCTION c_overpaid (EMP, integer) RETURNS boolean AS '
- DECLARE
- emprec ALIAS FOR $1;
- sallim ALIAS FOR $2;
- BEGIN
- IF emprec.salary ISNULL THEN
- RETURN ''f'';
- END IF;
- RETURN emprec.salary > sallim;
- END;
-' LANGUAGE 'plpgsql';
-</programlisting>
- </para>
+ <varlistentry>
+ <term><varname>TG_NARGS</varname></term>
+ <listitem>
+ <para>
+ Data type <type>integer</type>; the number of arguments given to the trigger
+ procedure in the <command>CREATE TRIGGER</command> statement.
+ </para>
+ </listitem>
+ </varlistentry>
- </example>
+ <varlistentry>
+ <term><varname>TG_ARGV[]</varname></term>
+ <listitem>
+ <para>
+ Data type array of <type>text</type>; the arguments from
+ the <command>CREATE TRIGGER</command> statement.
+ The index counts from 0 and can be given as an expression. Invalid
+ indices (< 0 or >= tg_nargs) result in a NULL value.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>
+ Second they must return either NULL or a record/row containing
+ exactly the structure of the table the trigger was fired for.
+ Triggers fired AFTER might always return a NULL value with no
+ effect. Triggers fired BEFORE signal the trigger manager
+ to skip the operation for this actual row when returning NULL.
+ Otherwise, the returned record/row replaces the inserted/updated
+ row in the operation. It is possible to replace single values directly
+ in NEW and return that or to build a complete new record/row to
+ return.
+ </para>
+ </sect2>
<example>
- <title>A PL/pgSQL Trigger Procedure</title>
+ <title>A PL/pgSQL Trigger Procedure Example</title>
<para>
- This trigger ensures that any time a row is inserted or updated
+ This trigger ensures, that any time a row is inserted or updated
in the table, the current user name and time are stamped into the
row. And it ensures that an employees name is given and that the
salary is a positive value.
-<programlisting>
CREATE TABLE emp (
empname text,
salary integer,
CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp
FOR EACH ROW EXECUTE PROCEDURE emp_stamp();
-</programlisting>
+ </programlisting>
+ </para>
+ </example>
+ </sect1>
+
+ <!-- **** PL/pgSQL Examples **** -->
+
+ <sect1 id="plpgsql-examples">
+ <title>Examples</title>
+
+ <para>
+ Here are only a few functions to demonstrate how easy it is to
+ write PL/pgSQL
+ functions. For more complex examples the programmer
+ might look at the regression test for PL/pgSQL.
+ </para>
+
+ <para>
+ One painful detail in writing functions in PL/pgSQL is the handling
+ of single quotes. The function's source text on <command>CREATE FUNCTION</command> must
+ be a literal string. Single quotes inside of literal strings must be
+ either doubled or quoted with a backslash. We are still looking for
+ an elegant alternative. In the meantime, doubling the single quotes
+ as in the examples below should be used. Any solution for this
+ in future versions of <productname>Postgres</productname> will be
+ forward compatible.
+ </para>
+ <para>
+ For a detailed explanation and examples of how to escape single
+ quotes in different situations, please see <xref linkend="plpgsql-quote"></xref> in
+ <xref linkend="plpgsql-porting">Porting From Oracle PL/SQL</xref>.
+ </para>
+
+ <example>
+ <title>A Simple PL/pgSQL Function to Increment an Integer</title>
+
+ <para>
+ The following two PL/pgSQL functions are identical to their
+ counterparts from the C language function discussion. This
+ function receives an <type>integer</type> and increments it by
+ one, returning the incremented value.
+ </para>
+
+ <programlisting>
+CREATE FUNCTION add_one (integer) RETURNS integer AS '
+ BEGIN
+ RETURN $1 + 1;
+ END;
+' LANGUAGE 'plpgsql';
+ </programlisting>
+ </example>
+
+ <example>
+ <title>A Simple PL/pgSQL Function to Concatenate Text</title>
+
+ <para>
+ This function receives two <type>text</type> parameters and
+ returns the result of concatenating them.
</para>
+
+ <programlisting>
+CREATE FUNCTION concat_text (text, text) RETURNS text AS '
+ BEGIN
+ RETURN $1 || $2;
+ END;
+' LANGUAGE 'plpgsql';
+ </programlisting>
</example>
+
+ <example>
+ <title>A PL/pgSQL Function on Composite Type</title>
+
+ <para>
+ In this example, we take EMP (a table) and an <type>integer</type> as
+ arguments to our function, which returns a <type>boolean</type>. If the
+ "salary" field of the EMP table is <literal>NULL</literal>, we return
+ "f". Otherwise we compare with that field with the <type>integer</type>
+ passed to the function and return the <type>boolean</type> result of the
+ comparison (t or f). This is the PL/pgSQL equivalent to the
+ example from the C functions.
+ </para>
+ <para>
+ <programlisting>
+CREATE FUNCTION c_overpaid (EMP, integer) RETURNS boolean AS '
+ DECLARE
+ emprec ALIAS FOR $1;
+ sallim ALIAS FOR $2;
+ BEGIN
+ IF emprec.salary ISNULL THEN
+ RETURN ''f'';
+ END IF;
+ RETURN emprec.salary > sallim;
+ END;
+' LANGUAGE 'plpgsql';
+ </programlisting>
+ </para>
+ </example>
</sect1>
+ <!-- **** Porting from Oracle PL/SQL **** -->
+
<sect1 id="plpgsql-porting">
<sect1info>
<listitem>
<para>
In PostgreSQL you <emphasis>need</emphasis> to escape single
- quotes. See <xref linkend="plpgsql-quote">.
+ quotes. See <xref linkend="plpgsql-quote"></xref>.
</para>
</listitem>
</itemizedlist>
In PostgreSQL you need to escape single quotes inside your
function definition. This can lead to quite amusing code at
times, especially if you are creating a function that generates
- other function(s), as in <xref
- linkend="plpgsql-porting-nastyquote">. One thing to keep in mind
+ other function(s), as in
+ <xref linkend="plpgsql-porting-nastyquote">this example</xref>.
+ One thing to keep in mind
when escaping lots of single quotes is that, except for the
beginning/ending quotes, all the others will come in even
quantity.
</para>
<para>
- <xref linkend="plpgsql-quoting-table"> gives the scoop. (You'll
+ <xref linkend="plpgsql-quoting-table"></xref> gives the scoop. (You'll
love this little chart.)
</para>
(which accounts for 8 quotes) <emphasis>and</emphasis>
terminate that string (2 more). You will probably only need
that if you were using a function to generate other functions
- (like in <xref linkend="plpgsql-porting-nastyquote">).
+ (like in <xref linkend="plpgsql-porting-nastyquote"></xref>).
</entry>
<entry><programlisting>
a_output := a_output || '' if v_'' ||
On PostgreSQL functions are created using single quotes as
delimiters, so you have to escape single quotes inside your
functions (which can be quite annoying at times; see <xref
- linkend="plpgsql-quote">).
+ linkend="plpgsql-quote">this example</xref>).
</para>
</listitem>
<para>
The following Oracle PL/SQL procedure is used to parse a URL and
return several elements (host, path and query). It is an
- procedure because in functions only one value can be returned
- (see <xref linkend="plpgsql-porting-procedures">). In
+ procedure because in PL/pgSQL functions only one value can be returned
+ (see <xref linkend="plpgsql-porting-procedures"></xref>). In
PostgreSQL, one way to work around this is to split the procedure
in three different functions: one to return the host, another for
the path and another for the query.
I got tired of doing this and created my own
<function>instr</function> functions that behave exactly like
Oracle's (it makes life easier). See the <xref
- linkend="plpgsql-porting-appendix"> for the code.
+ linkend="plpgsql-porting-appendix"></xref> for the code.
</para>
</note>
</sect2>
create or replace procedure cs_create_job(v_job_id in integer)
is
a_running_job_count integer;
- pragma autonomous_transaction;<co id="co.plpgsql-porting-pragma">
+ pragma autonomous_transaction;<co id="co.plpgsql-porting-pragma"></co>
begin
- lock table cs_jobs in exclusive mode;<co id="co.plpgsql-porting-locktable">
+ lock table cs_jobs in exclusive mode;<co id="co.plpgsql-porting-locktable"></co>
select count(*) into a_running_job_count from cs_jobs
where end_stamp is null;
if a_running_job_count > 0 then
- commit; -- free lock<co id="co.plpgsql-porting-commit">
+ commit; -- free lock<co id="co.plpgsql-porting-commit"></co>
raise_application_error(-20000, 'Unable to create a new job: a job is currently running.');
end if;
begin
insert into cs_jobs(job_id, start_stamp) values(v_job_id, sysdate);
- exception when dup_val_on_index then null; -- don't worry if it already exists<co id="co.plpgsql-porting-exception">
+ exception when dup_val_on_index then null; -- don't worry if it already exists<co id="co.plpgsql-porting-exception"></co>
end;
commit;
end;
insert into cs_jobs(job_id, start_stamp) values(v_job_id, sysdate());
return 1;
ELSE
- raise NOTICE ''Job already running.'';<co id="co.plpgsql-porting-raise">
+ raise NOTICE ''Job already running.'';<co id="co.plpgsql-porting-raise"></co>
END IF;
return 0;
nicely, but you have to remember to use
<function>quote_literal(TEXT)</function> and
<function>quote_string(TEXT)</function> as described in <xref
- linkend="plpgsql-statements">. Constructs of the type
+ linkend="plpgsql-statements"></xref>. Constructs of the type
<literal>EXECUTE ''SELECT * from $1'';</literal> will not work
unless you use these functions.
</para>
execution: <literal>iscachable</literal> (function always returns
the same result when given the same arguments) and
<literal>isstrict</literal> (function returns NULL if any
- argument is NULL). Consult the <literal>CREATE
- FUNCTION</literal> reference for details.
+ argument is NULL). Consult the <command>CREATE
+ FUNCTION</command> reference for details.
</para>
<para>
To make use of these optimization attributes, you have to use the
- <literal>WITH</literal> modifier in your <literal>CREATE
- FUNCTION</literal> statement. Something like:
+ <literal>WITH</literal> modifier in your <command>CREATE
+ FUNCTION</command> statement. Something like:
<programlisting>
CREATE FUNCTION foo(...) RETURNS integer AS '
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