From: | Zeugswetter Andreas DBT <Andreas(dot)Zeugswetter(at)telecom(dot)at> |
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To: | "'pgsql-hackers(at)hub(dot)org'" <pgsql-hackers(at)hub(dot)org> |
Subject: | Re: [HACKERS] Group By, NULL values and inconsistent behaviour. |
Date: | 1998-01-26 11:51:54 |
Message-ID: | 219F68D65015D011A8E000006F8590C6010A51A8@sdexcsrv1.sd.spardat.at |
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Lists: | pgsql-hackers |
>> In the second query, the first two rows have been grouped, but
shouldn't
>> they not be since b is NULL? I thought that NULL != NULL?
Note that:
NULL <> NULL is false
NULL = NULL is false
> select * from t1 x, t1 y where x.b <> y.b;
a b c a b c
No rows found.
> select * from t1 x, t1 y where x.b = y.b;
a b c a b c
No rows found.
> select * from t1 x, t1 y where not x.b = y.b;
a b c a b c
No rows found.
> select * from t1 x, t1 y where not x.b <> y.b;
a b c a b c
No rows found.
> select * from t1 where a = b;
a b c
No rows found.
> select * from t1 where a <> b;
a b c
No rows found.
>
The false seems not to be commutative.
Feel free to ask for more
Andreas
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