"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