I have two statements that accomplish the same task and I'm trying to decide
which to use. One uses a sub-select, and the other just does a few more joins.
I expect that giving the SELECT statement's themseleves won't get me much help, so
here is the output of the EXPLAIN query that I ran on both of them. I read
the FAQ on EXPLAIN a bit but I'm still confused.
So could somebody help me understand why it appears as though the first query
will run much faster (?) than the second?
--snip!--
Nested Loop (cost=81.80..114.17 rows=33 width=68)
InitPlan
-> Seq Scan on l_portal_statuses (cost=0.00..22.50 rows=10 width=4)
-> Merge Join (cost=81.80..86.63 rows=3 width=52)
-> Merge Join (cost=59.13..63.43 rows=33 width=44)
-> Sort (cost=22.67..22.67 rows=10 width=28)
-> Seq Scan on contacts m (cost=0.00..22.50 rows=10 width=28)
-> Sort (cost=36.47..36.47 rows=333 width=16)
-> Seq Scan on buildings b (cost=0.00..22.50 rows=333 width=16)
-> Sort (cost=22.67..22.67 rows=10 width=8)
-> Seq Scan on contracts c (cost=0.00..22.50 rows=10 width=8)
-> Index Scan using executives_pkey on executives e (cost=0.00..8.14 rows=10
width=16)
--------------------------------------------------------------------------------
Merge Join (cost=174.38..247.30 rows=333 width=76)
-> Index Scan using executives_pkey on executives e (cost=0.00..60.00 rows=1000
width=16)
-> Sort (cost=174.38..174.38 rows=33 width=60)
-> Merge Join (cost=167.58..173.53 rows=33 width=60)
-> Merge Join (cost=59.13..63.43 rows=33 width=44)
-> Sort (cost=22.67..22.67 rows=10 width=28)
-> Seq Scan on contacts m (cost=0.00..22.50 rows=10 width=28)
-> Sort (cost=36.47..36.47 rows=333 width=16)
-> Seq Scan on buildings b (cost=0.00..22.50 rows=333 width=16)
-> Sort (cost=108.44..108.44 rows=100 width=16)
-> Merge Join (cost=92.50..105.12 rows=100 width=16)
-> Sort (cost=69.83..69.83 rows=1000 width=12)
-> Seq Scan on contracts c (cost=0.00..20.00 rows=1000
width=12)
-> Sort (cost=22.67..22.67 rows=10 width=4)
-> Seq Scan on l_portal_statuses l (cost=0.00..22.50 rows=10
width=4)
--snip!--
Hopefully that's not too ugly.
TIA
-- Dave
