If at the sort step of the first query you expect to return 2178 rows,
why would you expect to return 1 row after self-joining those results
back on to the original table?
rms=# explain analyze
rms-# select * from
rms-# ( SELECT
rms(# host_id, max(mtime) as mtime
rms(# FROM
rms(# software_download
rms(# WHERE
rms(# bds_status_id not in (6,17,18)
rms(# GROUP BY
rms(# host_id, software_binary_id
rms(# ) latest_download
rms-# JOIN software_download using (host_id,mtime);
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------Merge
Join (cost=646.29..1346.89 rows=1 width=97) (actual time=126.815..225.881 rows=10870 loops=1) Merge Cond:
("outer".mtime= "inner".mtime) Join Filter: ("inner".host_id = "outer".host_id) -> Index Scan using sd_rht_1_idx on
software_download (cost=0.00..628.95 rows=13416 width=97) (actual time=0.018..28.508 rows=13416 loops=1) -> Sort
(cost=646.29..651.74rows=2178 width=12) (actual time=126.775..139.811 rows=10870 loops=1) Sort Key:
latest_download.mtime -> Subquery Scan latest_download (cost=476.53..525.54 rows=2178 width=12) (actual
time=49.643..95.524rows=10870 loops=1) -> HashAggregate (cost=476.53..503.76 rows=2178 width=16) (actual
time=49.639..69.748rows=10870 loops=1) -> Seq Scan on software_download (cost=0.00..377.78
rows=13167width=16) (actual time=0.006..24.266 rows=13167 loops=1) Filter: ((bds_status_id <>
6)AND (bds_status_id <> 17) AND (bds_status_id <> 18))Total runtime: 239.806 ms
(11 rows)
Robert Treat
--
Build A Brighter Lamp :: Linux Apache {middleware} PostgreSQL