Re: Confusion about locales and 'like' indexes

Dan Harris <fbsd(at)drivefaster(dot)net> writes:
> query that uses LIKE. In my research I have read that the locale
> setting may affect PostgreSQL's choice of seq scan vs index scan.

Non-C-locale indexes can't support LIKE because the sort ordering
isn't necessarily right.

> I am running Fedora Core 2 and it appears when I run "locale" that it
> is set to 'en.US-UTF-8'.

This is not a definitive indication of the environment the database
sees, though. Try "show lc_collate".

> I can pg_dump and initdb again with --locale=C if
> this will allow my LIKE queries to use indexes, but I just wanted to
> know if there was some other place I needed to change locales in the
> system? e.g. postgresql.conf or env vars? Or, would the initdb and
> reload alone fix it?

That would do it. Alternatively you can create special-purpose indexes
with one of the xxx_pattern_ops operator classes to support LIKE.

regards, tom lane