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Implement IS NOT DISTINCT FROM, update the regression tests and docs.

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Patch from Pavel Stehule, minor fixups by myself.
This commit is contained in:
Neil Conway
2005-12-11 10:54:28 +00:00
parent c10593149a
commit be8100d64e
4 changed files with 57 additions and 6 deletions
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18
doc/src/sgml/func.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.297 2005/12/03 16:45:05 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.298 2005/12/11 10:54:27 neilc Exp $
PostgreSQL documentation
-->
@ -345,16 +345,24 @@ PostgreSQL documentation
<indexterm>
<primary>IS DISTINCT FROM</primary>
</indexterm>
<indexterm>
<primary>IS NOT DISTINCT FROM</primary>
</indexterm>
The ordinary comparison operators yield null (signifying <quote>unknown</>)
when either input is null. Another way to do comparisons is with the
<literal>IS DISTINCT FROM</literal> construct:
<synopsis>
<replaceable>expression</replaceable> IS DISTINCT FROM <replaceable>expression</replaceable>
<replaceable>expression</replaceable> IS NOT DISTINCT FROM <replaceable>expression</replaceable>
</synopsis>
For non-null inputs this is the same as the <literal>&lt;&gt;</> operator.
However, when both inputs are null it will return false, and when just
one input is null it will return true. Thus it effectively acts as though
null were a normal data value, rather than <quote>unknown</>.
For non-null inputs, <literal>IS DISTINCT FROM</literal> this is
the same as the <literal>&lt;&gt;</> operator. However, when both
inputs are null it will return false, and when just one input is
null it will return true. Similarly, <literal>IS NOT DISTINCT
FROM</literal> is identical to <literal>=</literal> for non-null
inputs, returns true when both inputs are null, and false
otherwise. Thus, these constructs effectively act as though null
were a normal data value, rather than <quote>unknown</>.
</para>
<para>