Hi all, A question on how to read and interpret the explain analyse statement (and what to do)
I have a query "SELECT A.ordernummer, B.klantnummer FROM orders A LEFT OUTER JOIN klt_alg B ON A.Klantnummer=B.Klantnummer ORDER BY A.klantnummer;" Both tables have an btree index on klantnummer (int4, the column the join is on). I have vacuumed and analyzed both tables. The explain analyse is: QUERY PLAN Sort (cost=220539.32..223291.41 rows=1100836 width=12) (actual time=51834.128..56065.126 rows=1104380 loops=1) Sort Key: a.klantnummer -> Hash Left Join (cost=41557.43..110069.51 rows=1100836 width=12) (actual time=21263.858..42845.158 rows=1104380 loops=1) Hash Cond: (""outer"".klantnummer = ""inner"".klantnummer) -> Seq Scan on orders a (cost=0.00..46495.36 rows=1100836 width=8) (actual time=5.986..7378.488 rows=1104380 loops=1) -> Hash (cost=40635.14..40635.14 rows=368914 width=4) (actual time=21256.683..21256.683 rows=0 loops=1) -> Seq Scan on klt_alg b (cost=0.00..40635.14 rows=368914 width=4) (actual time=8.880..18910.120 rows=368914 loops=1) Total runtime: 61478.077 ms Questions: -> Hash Left Join (cost=41557.43..110069.51 rows=1100836 width=12) (actual time=21263.858..42845.158 rows=1104380 loops=1) 0. What exactly are the numbers in "cost=41557.43..110069.51" ( I assume for the other questions that 41557.43 is the estimated MS the query will take, what are the others)? 1. I assume that (cost=41557.43..110069.51 rows=1100836 width=12) is the estimated cost and (actual time=21263.858..42845.158 rows=1104380 loops=1) the actual cost. Is the difference acceptable? 2. If not, what can I do about it? Groeten, Joost Kraaijeveld Askesis B.V. Molukkenstraat 14 6524NB Nijmegen tel: 024-3888063 / 06-51855277 fax: 024-3608416 e-mail: [EMAIL PROTECTED] web: www.askesis.nl ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])