Hi, Thank you for the explanation, will optimize index, i've tried to add index on TANGGAL_CETAK, and it really work faster and as expected, showing index read as much as needed only, not all record.
On Tue, Jun 18, 2019 at 11:33 AM liviuslivius liviusliv...@poczta.onet.pl [firebird-support] <firebird-support@yahoogroups.com> wrote: > > > Hi > > If you have wher clause i that ordered query, > Think how you can do this on the paper. You have rows ordered you read > first and interesting is not null, you must skip it and go to next. And if > you must skip e.g 30 000 000 to read 1 000 000 then you see what is going > on. Always your indexes should satisfy your where clause. Above sample show > something called selectivity. You must maximize selectivity of index used.. > E.g. if you have only value true and false in the field then if your half > of the records are true and other half false then index can only slowdown > query execution. If you have 1000 records with true and 10000000 with false > index can speed up query looking for true and slowdown query looking for > false. > > Sumarize, index slowdown common value. > > Regards, > Karol Bieniaszewski > > >
