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Clarify description of our deviation from standard for temp tables,

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per suggestion from Mike Sykes.
This commit is contained in:
Tom Lane 2003-04-14 15:24:46 +00:00
parent 810e0b982b
commit 6d99dbb0c9
1 changed files with 25 additions and 17 deletions
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42
doc/src/sgml/ref/create_table.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.63 2003/03/25 16:15:39 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.64 2003/04/14 15:24:46 tgl Exp $
PostgreSQL documentation
-->
@ -826,24 +826,32 @@ CREATE TABLE distributors (
<title>Temporary Tables</title>
<para>
In addition to the local temporary table, SQL92 also defines a
<literal>CREATE GLOBAL TEMPORARY TABLE</literal> statement.
Global temporary tables are also visible to other sessions.
Although the syntax of <literal>CREATE TEMPORARY TABLE</literal>
resembles that of SQL92, the effect is not the same. In the standard,
temporary tables are associated with modules; a temporary table is created
just once and automatically exists (starting with empty contents) in every
session that uses the module.
<productname>PostgreSQL</productname> does not have modules, and
requires each session to issue its own <literal>CREATE TEMPORARY
TABLE</literal> command for each temporary table to be used.
</para>
<para>
For temporary tables, there is an optional <literal>ON COMMIT</literal> clause:
<synopsis>
CREATE { GLOBAL | LOCAL } TEMPORARY TABLE <replaceable class="parameter">table</replaceable> ( <replaceable class="parameter">...</replaceable> ) [ ON COMMIT { DELETE | PRESERVE } ROWS ]
</synopsis>
<note>
<para>
The spec-mandated behavior of temporary tables is widely ignored.
<productname>PostgreSQL</productname>'s behavior on this point is similar
to that of several other RDBMSs.
</para>
</note>
The <literal>ON COMMIT</literal> clause specifies whether or not
the temporary table should be emptied of rows whenever
<command>COMMIT</command> is executed. If the <literal>ON
COMMIT</> clause is omitted, SQL92 specifies that the default is
<literal>ON COMMIT DELETE ROWS</>. However, the behavior of
<productname>PostgreSQL</productname> is always like <literal>ON
COMMIT PRESERVE ROWS</literal>.
<para>
The optional <literal>ON COMMIT</literal> clause for temporary tables
also resembles SQL92, but has some differences.
If the <literal>ON COMMIT</> clause is omitted, SQL92 specifies that the
default behavior is <literal>ON COMMIT DELETE ROWS</>. However, the
default behavior in <productname>PostgreSQL</productname> is
<literal>ON COMMIT PRESERVE ROWS</literal>. The <literal>ON COMMIT
DROP</literal> option does not exist in SQL92 at all.
</para>
</refsect2>
@ -854,7 +862,7 @@ CREATE { GLOBAL | LOCAL } TEMPORARY TABLE <replaceable class="parameter">table</
The <literal>NULL</> <quote>constraint</quote> (actually a
non-constraint) is a <productname>PostgreSQL</productname>
extension to SQL92 that is included for compatibility with some
other RDBMS (and for symmetry with the <literal>NOT
other RDBMSs (and for symmetry with the <literal>NOT
NULL</literal> constraint). Since it is the default for any
column, its presence is simply noise.
</para>