index 4b85072aaee1fa256be8850040544bf6bb549936..3381c1db9963af3a79f93d9a8fce9538cb7a7844 100644 (file)
<!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/create_function.sgml,v 1.69 2006年11月03日 07:17:36 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_function.sgml,v 1.70 2006年11月10日 20:52:18 tgl Exp $
-->
<refentry id="SQL-CREATEFUNCTION">
<listitem>
<para>
- These attributes inform the system whether it is safe to
- replace multiple evaluations of the function with a single
- evaluation, for run-time optimization. At most one choice
+ These attributes inform the query optimizer about the behavior
+ of the function. At most one choice
may be specified. If none of these appear,
<literal>VOLATILE</literal> is the default assumption.
</para>
<para>
- <literal>IMMUTABLE</literal> indicates that the function always
+ <literal>IMMUTABLE</literal> indicates that the function
+ cannot modify the database and always
returns the same result when given the same argument values; that
is, it does not do database lookups or otherwise use information not
directly present in its argument list. If this option is given,
</para>
<para>
- <literal>STABLE</literal> indicates that within a single table scan
- the function will consistently
+ <literal>STABLE</literal> indicates that the function
+ cannot modify the database,
+ and that within a single table scan it will consistently
return the same result for the same argument values, but that its
result could change across SQL statements. This is the appropriate
selection for functions whose results depend on database lookups,