Miscellaneous other copy-editing.
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<chapter id="tutorial-advanced">
<para>
The behavior of foreign keys can be finely tuned to your
application. We will not go beyond this simple example in this
- tutorial, but just refer you to the <citetitle>Reference
- Manual</citetitle> for more information. Making correct use of
+ tutorial, but just refer you to &cite-reference;
+ for more information. Making correct use of
foreign keys will definitely improve the quality of your database
applications, so you are strongly encouraged to learn about them.
</para>
<productname>PostgreSQL</productname> has many features not
touched upon in this tutorial introduction, which has been
oriented toward newer users of <acronym>SQL</acronym>. These
- features are discussed in more detail in both the
- <citetitle>User's Guide</citetitle> and the
- <citetitle>Programmer's Guide</citetitle>.
+ features are discussed in more detail in both &cite-user;
+ and &cite-programmer;.
</para>
<para>
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ddl.sgml,v 1.5 2002/09/21 18:32:52 petere Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ddl.sgml,v 1.6 2002/10/20 05:05:46 tgl Exp $ -->
<chapter id="ddl">
<title>Data Definition</title>
explaining how tables are created and modified and what features are
available to control what data is stored in the tables.
Subsequently, we discuss how tables can be organized into
- namespaces, and how privileges can be assigned to tables. Finally,
+ schemas, and how privileges can be assigned to tables. Finally,
we will briefly look at other features that affect the data storage,
such as views, functions, and triggers. Detailed information on
these topics is found in &cite-programmer;.
<literal>second_column</literal> and the type <type>integer</type>.
The table and column names follow the identifier syntax explained
in <xref linkend="sql-syntax-identifiers">. The type names are
- also identifiers, but there are some exceptions. Note that the
+ usually also identifiers, but there are some exceptions. Note that the
column list is comma-separated and surrounded by parentheses.
</para>
<tip>
<para>
When you create many interrelated tables it is wise to choose a
- consistent naming patter for the tables and columns. For
+ consistent naming pattern for the tables and columns. For
instance, there is a choice of using singular or plural nouns for
table names, both of which are favored by some theorist or other.
</para>
</para>
<para>
- The default value may be a scalar expression, which well be
+ The default value may be a scalar expression, which will be
evaluated whenever the default value is inserted
(<emphasis>not</emphasis> when the table is created).
</para>
<para>
A foreign key constraint specifies that the values in a column (or
- a group of columns) must match the values in some other column.
+ a group of columns) must match the values appearing in some row
+ of another table.
We say this maintains the <firstterm>referential
integrity</firstterm> between two related tables.
</para>
<para>
Restricting and cascading deletes are the two most common options.
<literal>RESTRICT</literal> can also be written as <literal>NO
- ACTON</literal> and it's also the default if you don't specify
+ ACTION</literal> and it's also the default if you don't specify
anything. There are two other options for what should happen with
the foreign key columns when a primary key is deleted:
<literal>SET NULL</literal> and <literal>SET DEFAULT</literal>.
<para>Add columns,</para>
</listitem>
<listitem>
- <para>Remove a column,</para>
+ <para>Remove columns,</para>
</listitem>
<listitem>
<para>Add constraints,</para>
<para>Change default values,</para>
</listitem>
<listitem>
- <para>Rename a column,</para>
+ <para>Rename columns,</para>
</listitem>
<listitem>
- <para>Rename the table.</para>
+ <para>Rename tables.</para>
</listitem>
</itemizedlist>
</itemizedlist>
Schemas are analogous to directories at the operating system level,
- but schemas cannot be nested.
+ except that schemas cannot be nested.
</para>
<sect2 id="ddl-schemas-create">
(since this is one of the ways to restrict the activities of your
users to well-defined namespaces). The syntax for that is:
<programlisting>
-CREATE SCHEMA <replaceable>schemaname</replaceable> AUTHORIZATON <replaceable>username</replaceable>;
+CREATE SCHEMA <replaceable>schemaname</replaceable> AUTHORIZATION <replaceable>username</replaceable>;
</programlisting>
You can even omit the schema name, in which case the schema name
will be the same as the user name. See <xref
<para>
In the previous sections we created tables without specifying any
- schema names. Those tables (and other objects) are automatically
- put into a schema named <quote>public</quote>. Every new database
- contains such a schema. Thus, the following are equivalent:
+ schema names. By default, such tables (and other objects) are
+ automatically put into a schema named <quote>public</quote>. Every new
+ database contains such a schema. Thus, the following are equivalent:
<programlisting>
CREATE TABLE products ( ... );
</programlisting>
<para>
Schemas can be used to organize your data in many ways. There are
- a few usage patterns are recommended and are easily supported by
+ a few usage patterns that are recommended and are easily supported by
the default configuration:
<itemizedlist>
<listitem>
If you do not create any schemas then all users access the
public schema implicitly. This simulates the situation where
schemas are not available at all. This setup is mainly
- recommended when there is only a single user or few cooperating
+ recommended when there is only a single user or a few cooperating
users in a database. This setup also allows smooth transition
from the non-schema-aware world.
</para>
additional functions provided by third parties, etc.), put them
into separate schemas. Remember to grant appropriate
privileges to allow the other users to access them. Users can
- then refer to these additional object by qualifying the names
+ then refer to these additional objects by qualifying the names
with a schema name, or they can put the additional schemas into
their path, as they choose.
</para>
<screen>
DROP TABLE products CASCADE;
</screen>
- and all the dependent objects will be removed. Actually, this
+ and all the dependent objects will be removed. In this case, it
doesn't remove the orders table, it only removes the foreign key
- constraint.
+ constraint. (If you want to check what DROP ... CASCADE will do,
+ run DROP without CASCADE and read the NOTICEs.)
</para>
<para>
According to the SQL standard, specifying either
<literal>RESTRICT</literal> or <literal>CASCADE</literal> is
required. No database system actually implements it that way, but
- the defaults might be different.
+ whether the default behavior is <literal>RESTRICT</literal> or
+ <literal>CASCADE</literal> varies across systems.
</para>
</note>
Foreign key constraint dependencies and serial column dependencies
from <productname>PostgreSQL</productname> versions prior to 7.3
are <emphasis>not</emphasis> maintained or created during the
- upgrade process. All other dependency types survive the upgrade.
+ upgrade process. All other dependency types will be properly
+ created during an upgrade.
</para>
</note>
</sect1>
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/dml.sgml,v 1.1 2002/08/05 19:44:57 petere Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/dml.sgml,v 1.2 2002/10/20 05:05:46 tgl Exp $ -->
<chapter id="dml">
<title>Data Manipulation</title>
necessarily possible to directly specify which row to update.
Instead, you specify which conditions a row must meet in order to
be updated. Only if you have a primary key in the table (no matter
- whether you declared it or not) you can address rows individually
- by choosing a condition that matches the primary key only.
+ whether you declared it or not) can you reliably address individual rows,
+ by choosing a condition that matches the primary key.
Graphical database access tools rely on this fact to allow you to
update rows individually.
</para>
DELETE FROM products WHERE price = 10;
</programlisting>
</para>
+
+ <para>
+ If you simply write
+<programlisting>
+DELETE FROM products;
+</programlisting>
+ then all rows in the table will be deleted! Caveat programmer.
+ </para>
</sect1>
</chapter>
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/queries.sgml,v 1.17 2002/09/20 18:39:41 petere Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/queries.sgml,v 1.18 2002/10/20 05:05:46 tgl Exp $ -->
<chapter id="queries">
<title>Queries</title>
<literal>table1</literal>. (The method of retrieval depends on the
client application. For example, the
<application>psql</application> program will display an ASCII-art
- table on the screen, client libraries will offer functions to
+ table on the screen, while client libraries will offer functions to
retrieve individual rows and columns.) The select list
specification <literal>*</literal> means all columns that the table
expression happens to provide. A select list can also select a
- subset of the available columns or even make calculations on the
- columns before retrieving them; see <xref
- linkend="queries-select-lists">. For example, if
+ subset of the available columns or make calculations using the
+ columns. For example, if
<literal>table1</literal> has columns named <literal>a</>,
<literal>b</>, and <literal>c</> (and perhaps others) you can make
the following query:
</programlisting>
(assuming that <literal>b</> and <literal>c</> are of a numerical
data type).
+ See <xref linkend="queries-select-lists"> for more details.
</para>
<para>
SELECT 3 * 4;
</programlisting>
This is more useful if the expressions in the select list return
- varying results. For example, you could call a function this way.
+ varying results. For example, you could call a function this way:
<programlisting>
SELECT random();
</programlisting>
<para>
First, an inner join is performed. Then, for each row in
T1 that does not satisfy the join condition with any row in
- T2, a joined row is returned with null values in columns of
+ T2, a joined row is added with null values in columns of
T2. Thus, the joined table unconditionally has at least
one row for each row in T1.
</para>
<para>
First, an inner join is performed. Then, for each row in
T2 that does not satisfy the join condition with any row in
- T1, a joined row is returned with null values in columns of
+ T1, a joined row is added with null values in columns of
T1. This is the converse of a left join: the result table
will unconditionally have a row for each row in T2.
</para>
<para>
First, an inner join is performed. Then, for each row in
T1 that does not satisfy the join condition with any row in
- T2, a joined row is returned with null values in columns of
+ T2, a joined row is added with null values in columns of
T2. Also, for each row of T2 that does not satisfy the
join condition with any row in T1, a joined row with null
- values in the columns of T1 is returned.
+ values in the columns of T1 is added.
</para>
</listitem>
</varlistentry>
<literal>JOIN</> syntax in the <literal>FROM</> clause is
probably not as portable to other SQL database products. For
outer joins there is no choice in any case: they must be done in
- the <literal>FROM</> clause. A <literal>ON</>/<literal>USING</>
+ the <literal>FROM</> clause. An <literal>ON</>/<literal>USING</>
clause of an outer join is <emphasis>not</> equivalent to a
<literal>WHERE</> condition, because it determines the addition
of rows (for unmatched input rows) as well as the removal of rows
<para>
In the second query, we could not have written <literal>SELECT *
- FROM test1 GROUP BY x;</literal>, because there is no single value
+ FROM test1 GROUP BY x</literal>, because there is no single value
for the column <literal>y</> that could be associated with each
group. In general, if a table is grouped, columns that are not
used in the grouping cannot be referenced except in aggregate
- expressions, for example:
+ expressions. An example with aggregate expressions is:
<screen>
<prompt>=></> <userinput>SELECT x, sum(y) FROM test1 GROUP BY x;</>
x | sum
they have a known constant value per group.
</para>
- <note>
+ <tip>
<para>
Grouping without aggregate expressions effectively calculates the
set of distinct values in a column. This can also be achieved
using the <literal>DISTINCT</> clause (see <xref
linkend="queries-distinct">).
</para>
- </note>
+ </tip>
<para>
- Here is another example: A <function>sum(sales)</function> on a
+ Here is another example: <function>sum(sales)</function> on a
table grouped by product code gives the total sales for each
product, not the total sales on all products.
<programlisting>
SELECT product_id, p.name, (sum(s.units) * p.price) AS sales
FROM products p LEFT JOIN sales s USING (product_id)
- GROUP BY pid, p.name, p.price;
+ GROUP BY product_id, p.name, p.price;
</programlisting>
- In this example, the columns <literal>pid</literal>,
+ In this example, the columns <literal>product_id</literal>,
<literal>p.name</literal>, and <literal>p.price</literal> must be
in the <literal>GROUP BY</> clause since they are referenced in
the query select list. (Depending on how exactly the products
SELECT <replaceable>select_list</replaceable> FROM ... <optional>WHERE ...</optional> GROUP BY ... HAVING <replaceable>boolean_expression</replaceable>
</synopsis>
Expressions in the <literal>HAVING</> clause can refer both to
- grouped expressions and to ungrouped expression (which necessarily
+ grouped expressions and to ungrouped expressions (which necessarily
involve an aggregate function).
</para>
Again, a more realistic example:
<programlisting>
SELECT product_id, p.name, (sum(s.units) * (p.price - p.cost)) AS profit
- FROM products p LEFT JOIN sales s USING (pid)
+ FROM products p LEFT JOIN sales s USING (product_id)
WHERE s.date > CURRENT_DATE - INTERVAL '4 weeks'
GROUP BY product_id, p.name, p.price, p.cost
HAVING sum(p.price * s.units) > 5000;
<para>
If more than one sort column is specified, the later entries are
used to sort rows that are equal under the order imposed by the
- earlier sort specifications.
+ earlier sort columns.
</para>
</sect1>
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<chapter id="tutorial-sql">
Constants that are not simple numeric values usually must be
surrounded by single quotes (<literal>'</>), as in the example.
The
- <type>date</type> column is actually quite flexible in what it
+ <type>date</type> type is actually quite flexible in what it
accepts, but for this tutorial we will stick to the unambiguous
format shown here.
</para>
where the file name for the source file must be available to the
backend server machine, not the client, since the backend server
reads the file directly. You can read more about the
- <command>COPY</command> command in the <citetitle>Reference
- Manual</citetitle>.
+ <command>COPY</command> command in &cite-reference;.
</para>
</sect1>
<indexterm><primary>duplicate</primary></indexterm>
As a final note, you can request that the results of a select can
- be returned in sorted order or with duplicate rows removed. (Just
- to make sure the following won't confuse you,
- <literal>DISTINCT</literal> and <literal>ORDER BY</literal> can be
- used separately.)
+ be returned in sorted order or with duplicate rows removed:
<programlisting>
SELECT DISTINCT city
San Francisco
(2 rows)
</screen>
+
+ <literal>DISTINCT</literal> and <literal>ORDER BY</literal> can be
+ used separately, of course.
</para>
</sect1>
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-->
<chapter id="tutorial-start">
<para>
If you are installing <productname>PostgreSQL</productname>
- yourself, then refer to the <citetitle>Administrator's
- Guide</citetitle> for instructions on installation, and return to
+ yourself, then refer to &cite-admin;
+ for instructions on installation, and return to
this guide when the installation is complete. Be sure to follow
closely the section about setting up the appropriate environment
variables.
<para>
The user's client (frontend) application that wants to perform
database operations. Client applications can be very diverse
- in nature: They could be a text-oriented tool, a graphical
+ in nature: a client could be a text-oriented tool, a graphical
application, a web server that accesses the database to
display web pages, or a specialized database maintenance tool.
Some client applications are supplied with the
<para>
Writing a custom application, using one of the several
available language bindings. These possibilities are discussed
- further in <citetitle>The PostgreSQL Programmer's
- Guide</citetitle>.
+ further in &cite-programmer;.
</para>
</listitem>
</itemizedlist>
<prompt>mydb=></prompt> <userinput>SELECT version();</userinput>
version
----------------------------------------------------------------
- PostgreSQL 7.2devel on i586-pc-linux-gnu, compiled by GCC 2.96
+ PostgreSQL 7.3devel on i586-pc-linux-gnu, compiled by GCC 2.96
(1 row)
<prompt>mydb=></prompt> <userinput>SELECT current_date;</userinput>
date
------------
- 2001-08-31
+ 2002-08-31
(1 row)
<prompt>mydb=></prompt> <userinput>SELECT 2 + 2;</userinput>
and <command>psql</command> will quit and return you to your
command shell. (For more internal commands, type
<literal>\?</literal> at the <command>psql</command> prompt.) The
- full capabilities of <command>psql</command> are documented in the
-
<citetitle>Reference Manual</citetitle>. If <productname>PostgreSQL</> is
+ full capabilities of <command>psql</command> are documented in
+
&cite-reference;. If <productname>PostgreSQL</> is
installed correctly you can also type <literal>man psql</literal>
at the operating system shell prompt to see the documentation. In
this tutorial we will not use these features explicitly, but you
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<chapter id="sql-syntax">
a <token>SET</token> token to appear in a certain position, and
this particular variation of <command>INSERT</command> also
requires a <token>VALUES</token> in order to be complete. The
- precise syntax rules for each command are described in the
- <citetitle>Reference Manual</citetitle>.
+ precise syntax rules for each command are described in
+ &cite-reference;.
</para>
<sect2 id="sql-syntax-identifiers">
</indexterm>
<para>
- There are four kinds of <firstterm>implicitly-typed
+ There are three kinds of <firstterm>implicitly-typed
constants</firstterm> in <productname>PostgreSQL</productname>:
- strings, bit strings, integers, and floating-point numbers.
+ strings, bit strings, and numbers.
Constants can also be specified with explicit types, which can
enable more accurate representation and more efficient handling by
the system. The implicit constants are described below; explicit
<programlisting>
SELECT 'foo' 'bar';
</programlisting>
- is not valid syntax, and <productname>PostgreSQL</productname> is
- consistent with <acronym>SQL9x</acronym> in this regard.
+ is not valid syntax. (This slightly bizarre behavior is specified
+ by <acronym>SQL9x</acronym>; <productname>PostgreSQL</productname> is
+ following the standard.)
</para>
</sect3>
opening quote (no intervening whitespace), e.g.,
<literal>B'1001'</literal>. The only characters allowed within
bit-string constants are <literal>0</literal> and
- <literal>1</literal>. Bit-string constants can be continued
- across lines in the same way as regular string constants.
+ <literal>1</literal>.
</para>
- </sect3>
- <sect3>
- <title>Integer Constants</title>
+ <para>
+ Alternatively, bit-string constants can be specified in hexadecimal
+ notation, using a leading <literal>X</literal> (upper or lower case),
+ e.g., <literal>X'1FF'</literal>. This notation is equivalent to
+ a bit-string constant with four binary digits for each hex digit.
+ </para>
<para>
- Integer constants in SQL are sequences of decimal digits (0
- though 9) with no decimal point and no exponent. The range of legal values
- depends on which integer data type is used, but the plain
- <type>integer</type> type accepts values ranging from -2147483648
- to +2147483647. (The optional plus or minus sign is actually a
- separate unary operator and not part of the integer constant.)
+ Both forms of bit-string constant can be continued
+ across lines in the same way as regular string constants.
</para>
</sect3>
<sect3>
- <title>Floating-Point Constants</title>
+ <title>Numeric Constants</title>
<indexterm>
- <primary>floating point</primary>
+ <primary>numeric</primary>
<secondary>constants</secondary>
</indexterm>
<para>
- Floating-point constants are accepted in these general forms:
+ Numeric constants are accepted in these general forms:
<synopsis>
+<replaceable>digits</replaceable>
<replaceable>digits</replaceable>.<optional><replaceable>digits</replaceable></optional><optional>e<optional>+-</optional><replaceable>digits</replaceable></optional>
<optional><replaceable>digits</replaceable></optional>.<replaceable>digits</replaceable><optional>e<optional>+-</optional><replaceable>digits</replaceable></optional>
<replaceable>digits</replaceable>e<optional>+-</optional><replaceable>digits</replaceable>
</synopsis>
where <replaceable>digits</replaceable> is one or more decimal
- digits. At least one digit must be before or after the decimal
- point. At least one digit must follow the exponent delimiter
- (<literal>e</literal>) if that field is present.
- Thus, a floating-point constant is distinguished from an integer
- constant by the presence of either the decimal point or the
- exponent clause (or both). There must not be a space or other
- characters embedded in the constant.
+ digits (0 through 9). At least one digit must be before or after the
+ decimal point, if one is used. At least one digit must follow the
+ exponent marker (<literal>e</literal>), if one is present.
+ There may not be any spaces or other characters embedded in the
+ constant. Notice that any leading plus or minus sign is not actually
+ considered part of the constant; it is an operator applied to the
+ constant.
</para>
<para>
- These are some examples of valid floating-point constants:
+ These are some examples of valid numeric constants:
<literallayout>
+42
3.5
4.
.001
</para>
<para>
- Floating-point constants are of type <type>DOUBLE
- PRECISION</type>. <type>REAL</type> can be specified explicitly
- by using <acronym>SQL</acronym> string notation or
- <productname>PostgreSQL</productname> type notation:
+ A numeric constant that contains neither a decimal point nor an
+ exponent is initially presumed to be type <type>integer</> if its
+ value fits in type <type>integer</> (32 bits); otherwise it is
+ presumed to be type <type>bigint</> if its
+ value fits in type <type>bigint</> (64 bits); otherwise it is
+ taken to be type <type>numeric</>. Constants that contain decimal
+ points and/or exponents are always initially presumed to be type
+ <type>numeric</>.
+ </para>
+
+ <para>
+ The initially assigned data type of a numeric constant is just a
+ starting point for the type resolution algorithms. In most
+ cases the constant will be automatically coerced to the most
+ appropriate type depending on context. When necessary, you
+ can force a numeric value to be interpreted as a specific
+ data type by casting it. For example, you can force a numeric
+ value to be treated as type <type>real</> (<type>float4</>)
+ by writing
<programlisting>
REAL '1.23' -- string style
-'1.23'::REAL -- PostgreSQL (historical) style
+1.23::REAL -- PostgreSQL (historical) style
</programlisting>
</para>
</sect3>
table (possibly qualified), or an alias for a table defined by means of a
FROM clause, or
the key words <literal>NEW</literal> or <literal>OLD</literal>.
- (NEW and OLD can only appear in the action portion of a rule,
+ (NEW and OLD can only appear in rules,
while other correlation names can be used in any SQL statement.)
The correlation name and separating dot may be omitted if the column name
is unique
<para>
A positional parameter reference is used to indicate a parameter
- in an SQL function. Typically this is used in SQL function
- definition statements. The form of a parameter is:
+ that is supplied externally to an SQL statement. Parameters are
+ used in SQL function definitions and in prepared queries.
+ The form of a parameter reference is:
<synopsis>
$<replaceable>number</replaceable>
</synopsis>
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<book id="tutorial">
</para>
<para>
- After you have worked through this tutorial you might want to move on
- to reading the <![%single-book;[<citetitle>User's
- Guide</citetitle>]]><![%set-of-books;[<xref linkend="user">]]> to
- gain a more formal knowledge of the SQL language, or the
- <![%single-book;[<citetitle>Programmer's
- Guide</citetitle>]]><![%set-of-books;[<xref linkend="programmer">]]>
- for information about developing applications for
+ After you have worked through this tutorial you might want to move on to
+ reading &cite-user; to gain a more formal knowledge of the SQL language,
+ or &cite-programmer; for information about developing applications for
<productname>PostgreSQL</productname>.
</para>
projects / postgresql / commitdiff