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Add note that COALESCE and NULLIF are shorthand forms of CASE.

This commit is contained in:
Tom Lane 2000-12-16 18:33:13 +00:00
parent cf00d59335
commit d316f22267
1 changed files with 14 additions and 1 deletions
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15
doc/src/sgml/func.sgml
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@ -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>