>> 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
 

Mon, 26 Jan 1998 12:51:54 +0100
Zeugswetter Andreas DBT <Andreas.Zeugswetter@telecom.at>
Re: [HACKERS] Group By, NULL values and inconsistent behaviour.