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This patch improves the documentation for SERIAL columns a little bit.

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Neil Conway
This commit is contained in:
Bruce Momjian 2002-12-06 05:17:42 +00:00
parent 982b26c0a9
commit da1738a178
1 changed files with 39 additions and 21 deletions
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doc/src/sgml/datatype.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.109 2002/11/21 23:31:20 tgl Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.110 2002/12/06 05:17:42 momjian Exp $
-->
<chapter id="datatype">
@ -654,10 +654,11 @@ NUMERIC
</indexterm>
<para>
The <type>serial</type> data types are not truly types, but are a
notational convenience for setting up unique identifier columns
in tables.
In the current implementation, specifying
The <type>serial</type> data type is not a true type, but merely
a notational convenience for setting up identifier columns
(similar to the <literal>AUTO_INCREMENT</literal> property
supported by some other databases). In the current
implementation, specifying
<programlisting>
CREATE TABLE <replaceable class="parameter">tablename</replaceable> (
@ -683,33 +684,50 @@ CREATE TABLE <replaceable class="parameter">tablename</replaceable> (
not automatic.
</para>
<para>
To use a <type>serial</type> column to insert the next value of
the sequence into the table, specify that the <type>serial</type>
column should be assigned the default value. This can be done
either be excluding from the column from the list of columns in
the <command>INSERT</command> statement, or through the use of
the <literal>DEFAULT</literal> keyword.
</para>
<para>
The type names <type>serial</type> and <type>serial4</type> are
equivalent: both create <type>integer</type> columns. The type
names <type>bigserial</type> and <type>serial8</type> work just
the same way, except that they create a <type>bigint</type>
column. <type>bigserial</type> should be used if you anticipate
the use of more than 2<superscript>31</> identifiers over the lifetime of the table.
the use of more than 2<superscript>31</> identifiers over the
lifetime of the table.
</para>
<para>
The sequence created by a <type>serial</type> type is automatically
dropped when
the owning column is dropped, and cannot be dropped otherwise.
(This was not true in <productname>PostgreSQL</productname> releases
before 7.3. Note that this automatic drop linkage will not occur for a
sequence created by reloading a dump from a pre-7.3 database; the dump
file does not contain the information needed to establish the dependency
link.)
The sequence created by a <type>serial</type> type is
automatically dropped when the owning column is dropped, and
cannot be dropped otherwise. (This was not true in
<productname>PostgreSQL</productname> releases before 7.3. Note
that this automatic drop linkage will not occur for a sequence
created by reloading a dump from a pre-7.3 database; the dump
file does not contain the information needed to establish the
dependency link.) Furthermore, this dependency between sequence
and column is made only for the <type>serial</> column itself; if
any other columns reference the sequence (perhaps by manually
calling the <function>nextval()</>) function), they may be broken
if the sequence is removed. Using <type>serial</> columns in
fashion is considered bad form.
</para>
<note><para>
Prior to <productname>PostgreSQL</productname> 7.3, <type>serial</type>
implied <literal>UNIQUE</literal>. This is no longer automatic. If
you wish a serial column to be <literal>UNIQUE</literal> or a
<literal>PRIMARY KEY</literal> it must now be specified, same as with
any other data type.
</para></note>
<note>
<para>
Prior to <productname>PostgreSQL</> 7.3, <type>serial</type>
implied <literal>UNIQUE</literal>. This is no longer automatic.
If you wish a serial column to be <literal>UNIQUE</literal> or a
<literal>PRIMARY KEY</literal> it must now be specified, just as
with any other data type.
</para>
</note>
</sect2>
</sect1>