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Document that NOT NULL domain constraints are not always honored.

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This commit is contained in:
Bruce Momjian 2010-05-29 19:06:16 +00:00
parent 23e9fe0391
commit d800b036d2
1 changed files with 7 additions and 2 deletions
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9
doc/src/sgml/ref/create_domain.sgml
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@ -1,5 +1,5 @@
<!-- <!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_domain.sgml,v 1.34 2010/04/03 07:22:58 petere Exp $ $PostgreSQL: pgsql/doc/src/sgml/ref/create_domain.sgml,v 1.35 2010/05/29 19:06:16 momjian Exp $
PostgreSQL documentation PostgreSQL documentation
--> -->
@ -121,7 +121,12 @@ CREATE DOMAIN <replaceable class="parameter">name</replaceable> [ AS ] <replacea
<term><literal>NOT NULL</></term> <term><literal>NOT NULL</></term>
<listitem> <listitem>
<para> <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> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>