haman...@t-online.de wrote: Bjørn T Johansen wrote: >> I am trying to move a small system from Oracle to PostgreSQL and I have come >> upon a sql that runs >> really slow compared to on the Oracle database and I am not able to >> interpret why this is slow.
> I have experienced that some subqueries can be quite slow, and would suspect > the NOT IN > clause. I occasionally rewrite > NOT IN (select key from unwanted_candidates) > as > IN (select key from possible_candidates except select key from > unwanted_candidates) I would try to rewrite these clauses to NOT EXISTS, for example a.avlsnr Not In (Select avlsnr From dyr_pause_mot) could be NOT EXISTS (SELECT NULL FROM dyr_pause_mot WHERE avlsnr = a.avlsnr) This can be executed as anti-join and is often more efficient. Yours, Laurenz Albe -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
