Обсуждение: LIKE search with ending % not optimized in v8

Hello. I believe in earlier versions, a query of the
form
select attrib from ttt where attrib like 'foo%' would
be able to take advantage of an index. I have seen
this in the past. Currently I am using v8.0.3. From
what I can see is that the execultion plan seems to
use a seq scan and to totally ignore the index. Is
this the case?

-Aditya

On Wed, Jun 22, 2005 at 02:03:29AM -0700, Aditya Damle wrote:
>
> Hello. I believe in earlier versions, a query of the
> form
> select attrib from ttt where attrib like 'foo%' would
> be able to take advantage of an index. I have seen
> this in the past. Currently I am using v8.0.3. From
> what I can see is that the execultion plan seems to
> use a seq scan and to totally ignore the index. Is
> this the case?

8.0.3 can certainly use indexes for LIKE queries, but the planner
will choose a sequential scan if it thinks that would be faster.
Have you vacuumed and analyzed your tables?  Could you post the
EXPLAIN ANALYZE output of a query, once with enable_seqscan turned
on and once with it turned off?

See also "Operator Classes" in the "Indexes" chapter of the
documentation:

http://www.postgresql.org/docs/8.0/static/indexes-opclass.html

What locale are you using?

--
Michael Fuhr
http://www.fuhr.org/~mfuhr/