Bruno Wolff III <bruno@wolff.to> writes:
> On Tue, Sep 14, 2004 at 00:57:07 +0100,
>> CREATE TABLE x (id int4 NOT NULL);
>> SELECT count(*) from x WHERE x IS NULL;
>> Optimizator should rewrite "x IS NULL" to simple "false"
> Based on responses to other optimization requests I have seen, I think the
> answer to this one is going to be that it isn't worth paying the cost
> for every query to check for this case, since no one is going to write
> a query like this except by mistake.
There's been some speculation about making the optimizer aware of table
constraints in general (eg, CHECK constraints) but I tend to agree that
doing this only for NOT NULL isn't very exciting.
regards, tom lane