in this case I can't replace FOR EXECUTE STATEMENT 'SELECT.. ' with FOR SELECT.. because is much slower thanks
From: "Dmitry Yemanov [email protected] [firebird-support]" <[email protected]> To: [email protected] Sent: Wednesday, August 19, 2015 4:18 PM Subject: [firebird-support] Re: MAKE 'EXECUTE STATEMENT' USE INDEX 19.08.2015 14:29, 'Mr. John' wrote: > This time,adding condition this way WHERE FIEL1=:F1 AND FIEL2=:F2 AND > * (FIEL3=:F3 OR **:F3 IS NULL) * INTO .. DO .. > > is causing query to be much slower ... > > this WHERE FIEL1=:F1 AND FIEL2=:F2 AND * (FIEL3=:F3 **) * INTO .. DO .. > takes *0.563s* because all three index segments are used for the retrieval. > but this takes *29.141s* > WHERE FIEL1=:F1 AND FIEL2=:F2 AND * (FIEL3=:F3 OR **:F3 IS NULL) * INTO > .. DO .. because (FIEL3=:F3 OR :F3 IS NULL) prevents the third index segment from being used, so only first two index segments are used for the retrieval. This is absolutely expected. 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