On Mon, Jul 13, 2009 at 1:33 PM, Tom Lane<t...@sss.pgh.pa.us> wrote: > Simon Riggs <si...@2ndquadrant.com> writes: >> In some cases, we have SQL being submitted that has superfluous >> self-joins. An example would be > >> select count(*) >> from foo1 a, foo1 b >> where a.c1 = b.c1 /* PK join */ >> and a.c2 = 5 >> and b.c2 = 10; > >> You may well ask who would be stupid enough to write SQL like that. The >> answer is of course that it is automatically generated by an ORM. > > Seems like the right answer is "fix the damn ORM". It's hard to believe > this sort of case comes up often enough to justify the cycles that would > be expended (on *every* join query) to try to recognize it.
I think it's more common than you might think. It's been requested on -performance within recent memory, and I've had cases where I needed to deal with it as well. You can't write: DELETE FROM table AS alias LEFT JOIN othertable ... so you end up writing: DELETE FROM table AS alias USING sametable LEFT JOIN othertable ... or sometimes: DELETE FROM table AS alias USING viewthatconstainstable ... ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
