Re: unique constraint - bug?

"Oliver Elphick" <olly@lfix.co.uk> writes:
> Tom Lane wrote:
>> Two nulls are never considered equal, therefore the unique constraint
>> does not trigger.

> I think you are not interpreting this right:

>         A unique constraint is satisfied if and only if no two rows in
>         a table have the same non-null values in the unique columns.

> I think it means that nulls are to be left out of account in the
> comparison.

Hmm.  What then of

        a, b, c
        a, NULL, c

If I "ignore the null" then these two rows are equal as well.

Still, you're right that it's a little more ambiguously worded than
I thought.  Can anyone check how other DBMSs handle this?

            regards, tom lane