On Wed, May 09, 2007 at 17:45:52 +0400, bash wrote: > > One index per table rule. At first glance it seems like SQLite could > > use at least one index for "x=5 OR y=7" case too, but there is no > > point in that, as the other part of the OR would require full table > > scan anyway. > > Why full table scan? :/ > SQLite can takes set (1) of rowid by ex(x) index for > "X=5". Then takes another set (2) of rowid by ex(y) for "Y=7". > Then SQLite need only to union this two set (1) and (2). > Final SQLite should returns rows where rowid in (set1 union set2).
You should read it the following way: "SQLite can't use two indexes per table, and using only one index is pointless, hence no index is used at all". So your question is actually "why SQLite uses at most one index per table?". My guess is that the benefits are out-weighted by the implementation complexity. -- Tomash Brechko ----------------------------------------------------------------------------- To unsubscribe, send email to [EMAIL PROTECTED] -----------------------------------------------------------------------------
