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Add documentation clarification for IS [NOT] NULL and row-valued

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expressions.
This commit is contained in:
Bruce Momjian 2008-04-07 00:51:27 +00:00
parent 347dd6a1cf
commit a84171b078
1 changed files with 6 additions and 2 deletions
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doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.427 2008/04/04 18:45:36 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.428 2008/04/07 00:51:27 momjian Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -344,7 +344,11 @@
<literal>IS NULL</> is true when the row expression itself is null
or when all the row's fields are null, while
<literal>IS NOT NULL</> is true when the row expression itself is non-null
and all the row's fields are non-null.
and all the row's fields are non-null. Because of this behavior,
<literal>IS NULL</> and <literal>IS NOT NULL</> do not always return
inverse results for row-valued expressions, i.e. a row-valued
expression that contains both NULL and non-null values will return false
for both tests.
This definition conforms to the SQL standard, and is a change from the
inconsistent behavior exhibited by <productname>PostgreSQL</productname>
versions prior to 8.2.