> estimate that 139654 rows will match f_state = 'PA' in the right
No, 375342 is the actual number. Using the index does appear slower
(limited testing noted).
explain select count(*) from state_tst where f_state = 'PA'/
NOTICE: QUERY PLAN:
Aggregate (cost=277899.65..277899.65 rows=1 width=0)
-> Seq Scan on state_tst (cost=0.00..277550.51 rows=139654
width=0)
select count(*) from state_tst where f_state = 'PA'/
count
'375342'
Elapsed: 139 wallclock secs
set enable_seqscan = off/
explain select count(*) from state_tst where f_state = 'PA'/
NOTICE: QUERY PLAN:
Aggregate (cost=542303.53..542303.53 rows=1 width=0)
-> Index Scan using st_f_state_idx on state_tst
(cost=0.00..541954.39 rows=139654 width=0)
select count(*) from state_tst where f_state = 'PA'/
count
'375342'
Elapsed: 222 wallclock secs
Tom
On Wed, May 22, 2002 at 12:26:35AM -0400, Tom Lane wrote:
> "Thomas A. Lowery" <tlowery@stlowery.net> writes:
> > Can I force the use of an index?
>
> Try "set enable_seqscan = off". But on the basis of what you've shown,
> it's not obvious that an indexscan will be faster. Is the planner's
> estimate that 139654 rows will match f_state = 'PA' in the right
> ballpark?
>
> regards, tom lane
