Simon Slavin <[email protected]> wrote: > On 13 Sep 2011, at 1:07pm, François wrote: > >> Can we consider that creating an index for an integer field is a good >> practice if this field has at least 3 possible values ? Or more ? > > It's about chunkiness, and which of the values you're looking for. > > If all possible values are equally distributed, and you frequently look for a > particular value, the index will help even if you > have only two possible values. If you have almost all '2011' rows, and > you're searching for '2011', then the index won't help > much.
Actually, the break-even point is roughly 1/10: an index helps if you are selecting 10% or fewer of the records in the table; otherwise, a linear scan is faster. -- Igor Tandetnik _______________________________________________ sqlite-users mailing list [email protected] http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
