From 1f3fbced6502dbe0427331dfa47fed0f3c50b955 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 4309cbf520d..14a1c770a11 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -10060,6 +10060,16 @@ 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">