So, it will be quite a rare occurrence then that this could be of any benefit. Still nice to know this.
RBS On 3 Dec 2015 1:33 am, "Richard Hipp" <drh at sqlite.org> wrote: > On 12/2/15, Bart Smissaert <bart.smissaert at gmail.com> wrote: > >> and the SQLite query planner sometimes notes that length when > considering > > data shape > > > > In what situations does that happen? > > > > CREATE TABLE ex1(a INTEGER, b VARCHAR(5), c VARCHAR(5000)); > CREATE INDEX ex1b ON ex1(b); > CREATE INDEX ex1c ON ex1(c); > > SELECT * FROM ex1 WHERE b=?1 AND c=?2; > > The query planner is faced with the decision of whether to use the > ex1b or ex1c index. Statistics gathered by ANALYZE would normally > break this tie, but suppose ANALYZE has not been run, or suppose both > indexes are equally selective. In that case, SQLite would choose ex1b > since it guesses the keys would be shorter and will compare faster and > the fanout will be greater, and hence extb can be searched using fewer > CPU cycles. > > > > -- > D. Richard Hipp > drh at sqlite.org > _______________________________________________ > sqlite-users mailing list > sqlite-users at mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users >
