On 12/12/2013 04:36 PM, Tom Lane wrote: > BTW, on further thought, I'm afraid this is a bigger can of worms than > it appears. The remarks above presume that the subquery is simple enough > to be pulled up, which is the case in this example. It might not be too > hard to make that case work. But what if the subquery *isn't* simple > enough to be pulled up --- for instance, it includes grouping or > aggregation? Then there's no way to unify its WHERE clause with the upper > semijoin qual. At the very least, this breaks the uniqueify-then-do-a- > plain-join implementation strategy for semijoins.
After having thought about it further, I think I understand. > So I'm now thinking this patch isn't worth pursuing. Getting all the > corner cases right would be a significant amount of work, and in the > end it would only benefit strangely-written queries. Originally it seemed to me that I just (luckily) found a new opportunity for the existing infrastructure. To change the infrastructure because of this small feature would be exactly the opposite. Thanks for having taken a look at it. // Antonin Houska (Tony) -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
