From d53f7cf11658a3252a6fddf308b992b751379f09 Mon Sep 17 00:00:00 2001
From: Noah Misch <noah@leadboat.com>
Date: Wed, 26 Jun 2013 19:51:56 -0400
Subject: [PATCH] Document effect of constant folding on CASE.
Back-patch to all supported versions.
Laurenz Albe
---
doc/src/sgml/func.sgml | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 4c5af4b83c8..8cf53855616 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -10563,6 +10563,16 @@ SELECT a,
SELECT ... WHERE CASE WHEN x <> 0 THEN y/x > 1.5 ELSE false END;
</programlisting>
</para>
+
+ <note>
+ <para>
+ As described in <xref linkend="xfunc-volatility">, functions and
+ operators marked <literal>IMMUTABLE</literal> can be evaluated when
+ the query is planned rather than when it is executed. This means
+ that constant parts of a subexpression that is not evaluated during
+ query execution might still be evaluated during query planning.
+ </para>
+ </note>
</sect2>
<sect2 id="functions-coalesce-nvl-ifnull">
--
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