From: Noah Misch <noah@leadboat.com>
Date: Wed, 26 Jun 2013 23:51:56 +0000 (-0400)
Subject: Document effect of constant folding on CASE.
X-Git-Tag: REL9_4_BETA1~1431
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=d53f7cf11658a3252a6fddf308b992b751379f09;p=postgresql

Document effect of constant folding on CASE.

Back-patch to all supported versions.

Laurenz Albe
---

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 4c5af4b83c..8cf5385561 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -10563,6 +10563,16 @@ SELECT a,
 SELECT ... WHERE CASE WHEN x &lt;&gt; 0 THEN y/x &gt; 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">