From d316f2226738d91e00461f49f6bef16ae178954c Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 16 Dec 2000 18:33:13 +0000
Subject: [PATCH] Add note that COALESCE and NULLIF are shorthand forms of
 CASE.

---
 doc/src/sgml/func.sgml | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 5b3012625ea..48bdb2a5e1c 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -1,4 +1,4 @@
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.41 2000/12/14 22:30:56 petere Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.42 2000/12/16 18:33:13 tgl Exp $ -->
 
 <chapter id="functions">
  <title>Functions and Operators</title>
@@ -2618,6 +2618,19 @@ SELECT COALESCE(description, short_description, '(none)') ...
 SELECT NULLIF(value, '(none)') ...
 </programlisting>
   </para>
+
+  <tip>
+   <para>
+    <function>COALESCE</function> and <function>NULLIF</function> are
+    just shorthand for <token>CASE</token> expressions.  They are actually
+    converted into <token>CASE</token> expressions at a very early stage
+    of processing, and subsequent processing thinks it is dealing with
+    <token>CASE</token>.  Thus an incorrect <function>COALESCE</function> or
+    <function>NULLIF</function> usage may draw an error message that
+    refers to <token>CASE</token>.
+   </para>
+  </tip>
+
  </sect1>
 
 
-- 
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