Re: [HACKERS] Group By, NULL values and inconsistent behaviour. - Mailing list 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