Mikkel Lauritsen <renard(at)tala(dot)dk> writes:
> I would like to do a query which retrieves the newest record for each
> type, and the persistence framework that I'm using does something
> which is structurally like
> SELECT * FROM table t1 WHERE 0 = (SELECT COUNT(*) FROM table t2 WHERE
> t2.type = t1.type AND t2.timestamp > t1.timestamp)
I suspect that *any* database is going to have trouble optimizing that.
You'd be well advised to lobby the persistence framework's authors to
produce less brain-dead SQL. The NOT EXISTS formulation seems to
express what's wanted much less indirectly.
regards, tom lane