On Sunday 17 August 2003 16:39, Alexander M. Pravking wrote: > On Sun, Aug 17, 2003 at 11:32:58AM +0100, Richard Huxton wrote: > > Boiling the problem down, I've looked at a clause of the form: > > a OR (b AND c) > > which PG converts to: > > (a OR b) AND (a OR c)
> > Is it an artefact of displaying the EXPLAIN, or is it actually processed > > that way? You could see how testing "a" twice could be expensive in some > > situations. > > Looks like it actually works this way. > I had the same problem several weeks ago on 7.3.3 with 4 such OR's. > The final filter became monsterous, and the query was very slow. > > I've simply rewritten the query using UNION, and it became much faster. Doesn't seem to matter much in this case, although I tried it as a UNION just to check the results were the same. Thanks Alexander -- Richard Huxton Archonet Ltd ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
