From 5e74a427854fa17babfbb0e22c4ca95e4f48f2fe Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <andrew@dunslane.net>
Date: Mon, 11 Mar 2019 18:14:05 -0400
Subject: [PATCH] Document incompatibility of comparison expressions with
 VARIADIC array arguments

COALESCE, GREATEST and LEAST all look like functions taking variable
numbers of arguments, but in fact they are not functions, and so
VARIADIC array arguments don't work with them. Add a note to the docs
explaining this fact.

The consensus is not to try to make this work, but just to document the
limitation.

Discussion: https://postgr.es/m/CAFj8pRCaAtuXuRtvXf5GmPbAVriUQrNMo7-=TXUFN025S31R_w@mail.gmail.com
---
 doc/src/sgml/func.sgml | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 03859a78eaa..7fbcdfeae56 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -12481,6 +12481,15 @@ SELECT setval('foo', 42, false);    <lineannotation>Next <function>nextval</func
    </para>
   </tip>
 
+   <note>
+    <para>
+     Although <token>COALESCE</token>, <token>GREATEST</token>, and
+     <token>LEAST</token> are syntactically similar to functions, they are
+     not strictly functions, and thus cannot be used with explicit
+     <token>VARIADIC</token> array arguments.
+    </para>
+   </note>
+
   <sect2 id="functions-case">
    <title><literal>CASE</literal></title>
 
-- 
2.39.5