"Stephan Szabo" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> select distinct on (att_2) * from test
> order by att_2, att_1 desc;
Yes that's right it's help me,
but here the optimizer have some problems:
CREATE VIEW last_user_logs AS
SELECT DISTINCT ON (id_user) *
FROM user_logs
ORDER BY id_user, id_user_log DESC;
and now:
# explain analyze select * from user_logs where id_user = '5430';
NOTICE: QUERY PLAN:
Index Scan using idx_user_user_logs on user_logs (cost=0.00..3038.59
rows=939 width=68) (actual time=0.03..0.03 rows=0 loops=1)
Total runtime: 0.12 msec
EXPLAIN
empdb=# explain analyze select * from last_user_logs where id_user = 5430;
NOTICE: QUERY PLAN:
Subquery Scan last_user_logs (cost=20256.12..20725.43 rows=18772 width=68)
(actual time=3526.10..3526.10 rows=0 loops=1)
-> Unique (cost=20256.12..20725.43 rows=18772 width=68) (actual
time=3067.14..3522.54 rows=2226 loops=1)
-> Sort (cost=20256.12..20256.12 rows=187723 width=68) (actual
time=3067.13..3241.94 rows=187723 loops=1)
-> Seq Scan on user_logs (cost=0.00..3813.23 rows=187723
width=68) (actual time=0.02..1070.59 rows=187723 loops=1)
Total runtime: 3578.07 msec
EXPLAIN
if I do instead without view and
#explain analyze SELECT DISTINCT ON (id_user) *
FROM user_logs
WHERE id_user = 5430
ORDER BY id_user, id_user_log DESC;
NOTICE: QUERY PLAN:
Unique (cost=3084.93..3087.27 rows=94 width=68) (actual time=0.21..0.21
rows=0 loops=1)
-> Sort (cost=3084.93..3084.93 rows=939 width=68) (actual
time=0.21..0.21 rows=0 loops=1)
-> Index Scan using idx_user_user_logs on user_logs
(cost=0.00..3038.59 rows=939 width=68) (actual time=0.03..0.03 rows=0
loops=1)
Total runtime: 0.31 msec
EXPLAIN
Ciao
Gaetano
---------------------------(end of broadcast)---------------------------
TIP 2: you can get off all lists at once with the unregister command
(send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
