David Rowley <dgrowleyml@xxxxxxxxx> writes: > It would be possible to have some sort of MergeExcept operator and > have the planner consider that. Unfortunately, since the upper planner > was changed a few years ago to have it consider paths the same as the > join planner does, nobody has yet come back to the union planner to > properly pathify that. I do have a WIP patch to do this work, but I > wasn't planning on improving EXCEPT, only UNION. Making it work for > EXCEPT and INTERSECT would require a new executor operator. Yeah. We're moderately good about UNION ALL, but UNION/INTERSECT/EXCEPT are an area that nobody has ever gotten around to optimizing: the two sub-queries will be planned independently and then fed to a simplistic set-operation node. Maybe that'll get better someday but don't hold your breath. In the meantime, try to recast an EXCEPT query as an antijoin. regards, tom lane
