From 2c2faa17f2c48477763d3c2db39aac29eb2f4909 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 10 Nov 2006 20:52:18 +0000
Subject: [PATCH] Emphasize that immutable and stable functions are not allowed
to modify the database. xfunc.sgml was already pretty definite on the point,
but it doesn't hurt to make it clear here too.
---
doc/src/sgml/ref/create_function.sgml | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/doc/src/sgml/ref/create_function.sgml b/doc/src/sgml/ref/create_function.sgml
index 4b85072aaee..3381c1db996 100644
--- a/doc/src/sgml/ref/create_function.sgml
+++ b/doc/src/sgml/ref/create_function.sgml
@@ -1,5 +1,5 @@
<!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/create_function.sgml,v 1.69 2006/11/03 07:17:36 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_function.sgml,v 1.70 2006/11/10 20:52:18 tgl Exp $
-->
<refentry id="SQL-CREATEFUNCTION">
@@ -198,15 +198,15 @@ CREATE [ OR REPLACE ] FUNCTION
<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,
@@ -215,8 +215,9 @@ CREATE [ OR REPLACE ] FUNCTION
</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,
--
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