Обсуждение: Equality operators on NULL values

(in)Equality operators evaluates to NULL when any of their
arguments are NULL as summarized bellow.
NULL=NULL ==> NULL1=NULL    ==> NULL1=1       ==> t1=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 ==> t1=NULL    ==> NULL (or anything else as long as it is not t)1=1       ==> t1=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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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