From cb0492c8c0eacb752b95896d01580a965a9bfc77 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Sat, 29 May 2010 19:06:16 +0000
Subject: [PATCH] Document that NOT NULL domain constraints are not always
 honored.

---
 doc/src/sgml/ref/create_domain.sgml | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/ref/create_domain.sgml b/doc/src/sgml/ref/create_domain.sgml
index 1342aa241f..93efac8bcc 100644
--- a/doc/src/sgml/ref/create_domain.sgml
+++ b/doc/src/sgml/ref/create_domain.sgml
@@ -121,7 +121,12 @@ CREATE DOMAIN <replaceable class="parameter">name</replaceable> [ AS ] <replacea
       <term><literal>NOT NULL</></term>
       <listitem>
        <para>
-        Values of this domain are not allowed to be null.
+        Values of this domain are normally prevented from being null.
+        However, it is still possible for a domain with this constraint
+        to take a null value if it is assigned a matching domain type
+        that has become null, e.g. via a LEFT OUTER JOIN, or
+        <command>INSERT INTO tab (domcol) VALUES ((SELECT domcol FROM
+        tab WHERE false))</command>.
        </para>
       </listitem>
      </varlistentry>
-- 
2.11.4.GIT