Hi,
I have a strange (for me) result ... Why the second request is really quicker
with a Seq Scan than the first one with a DISTINCT and using an index !?
The table have really 183957 rows ... not like the Seq Scan seems to
expect ... !? I understand nothing here ...
Thanks for your explanations ...
# explain analyze SELECT distinct s.id_category FROM site s;
QUERY
PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Unique (cost=0.00..11903.15 rows=56 width=4) (actual time=0.147..1679.170
rows=68 loops=1)
-> Index Scan using ix_site_id_category on site s (cost=0.00..11496.38
rows=162706 width=4) (actual time=0.143..1452.611 rows=183957 loops=1)
Total runtime: 1679.496 ms
(3 rows)
Time: 1680,810 ms
# explain analyze SELECT s.id_category FROM site s group by id_category;
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------
HashAggregate (cost=7307.83..7307.83 rows=56 width=4) (actual
time=1198.968..1199.084 rows=68 loops=1)
-> Seq Scan on site s (cost=0.00..6901.06 rows=162706 width=4) (actual
time=0.097..921.676 rows=183957 loops=1)
Total runtime: 1199.260 ms
(3 rows)
--
Bill Footcow
