On Thu, Dec 16, 2004 at 23:33:00 -0500, Greg Stark <[EMAIL PROTECTED]> wrote: > > Chris Smith <[EMAIL PROTECTED]> writes: > > > Would doing it this way require an index: > > > > create index lower_lastname on table x lower(lastname); > > Well it doesn't *require* but it may be a good idea. It depends on your > queries. It will NOT be useful for a query like: > > select * from x order by lower(lastname) > > where postgres won't bother with the index since it will be slower than just > resorting the entire table. The way this index is useful is if you have > queries of the form:
Using an index to do an order by is an order N operation. Doing a sort is an order N log N operation. For large values of N, a index will be faster. The index will slow down write operations, so it may still be a bad idea in some cases. ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
