Pavel Ivanov a écrit : >> It seems to me the DB engine tries to perform an unindexed search if the >> requested value is not present in the index. >> Is this behaviour intended ? How can I get rid of it ? >> > > If your index is in that very order as you said, i.e. (utc, > id_client), then whatever @IdClient you put in the query SQLite will > perform full index scan because it can benefit from index only for the > purpose of ordering but not for the purpose of searching. You've just > got lucky having LIMIT 1 in the query and providing @IdClient that has > some utc close to maximum. If you provide @IdClient that has utc close > to minimum then you'll get long execution time again. But if you > change your index to (id_client, utc) then you'll have fast times for > any @IdClient. > > That make perfectly sense, thank you very much ! I didn't imagine the fields' order could be important but I can clearly see now.
This might not be the scope of sqlite.org documentation area, but it could be a good idea to have a paper about how indexes work. Regards, _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
