Greg Stark <st...@enterprisedb.com> writes: > It's tempting to have Hash cheat and just peek at the node beneath it > to see if it's a HashAggregate, in which case it could call a special > method to request the whole hash. But it would have to know that it's > just a plain uniquify and not implementing a GROUP BY.
More to the point, it would have to check if it's unique-ifying on the same columns and with the same operators as the upper hash is using. If we were going to do something like this, making it a real option to the Hash node and teaching the planner about that would be *much* easier, and would also allow saner cost estimation. I agree that doing something like this on the inner side of a hashjoin might not be too unreasonable --- it was the mergejoin case that really seemed ugly when I thought about it. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers