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* Equality operators on NULL values
@ 2003-08-24 01:28 Bertrand Petit <pgsql-sql@phoe.frmug.org>
0 siblings, 1 reply; 2+ messages in thread
From: Bertrand Petit @ 2003-08-24 01:28 UTC (permalink / raw)
To: pgsql-sql
(in)Equality operators evaluates to NULL when any of their
arguments are NULL as summarized bellow.
NULL=NULL ==> NULL
1=NULL ==> NULL
1=1 ==> t
1=2 ==> f
I have a case where I need to delete rows from table A for records
that are designated in table B. One of the joined colum can have NULL
values. Therefore I need an operator behaving as follows:
NULL=NULL ==> t
1=NULL ==> NULL (or anything else as long as it is not t)
1=1 ==> t
1=2 ==> f
I replaced the use of the = operator with this expression:
nullif(tabA.col_with_nulls, tabB.col_with_nulls) IS NULL
It works correctly but the intent is not that clear.
Is there a stock replacement operator that would behave like
the second truth table?
Regards,
Bertrand.
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^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Equality operators on NULL values
@ 2003-08-24 08:43 Peter Eisentraut <peter_e@gmx.net>
parent: Bertrand Petit <pgsql-sql@phoe.frmug.org>
0 siblings, 0 replies; 2+ messages in thread
From: Peter Eisentraut @ 2003-08-24 08:43 UTC (permalink / raw)
To: Bertrand Petit <pgsql-sql@phoe.frmug.org>; +Cc: pgsql-sql
Bertrand Petit writes:
> NULL=NULL ==> t
> 1=NULL ==> NULL (or anything else as long as it is not t)
> 1=1 ==> t
> 1=2 ==> f
> Is there a stock replacement operator that would behave like
> the second truth table?
No, but why not write
(a = b) or (a is null and b is null)
--
Peter Eisentraut peter_e@gmx.net
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2003-08-24 01:28 Equality operators on NULL values Bertrand Petit <pgsql-sql@phoe.frmug.org>
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