Re: Why is my index not used

try to cast your argument, for example, if misscnt is of type bigint, try:

explain select * from cam where misscnt>=1::int8;


Best regards,
Chris

At 19:54 +0100 02/18/2002, Kristian Eide wrote:
>I have a table, currently at about 150.000 rows, with a btree index on a
>field named 'misscnt'. ~138k of the rows have this fields set as null, ~12k
>as 0, ~350 as 1, ~200 as 2 and ~150 as 3 (these are the only values used).
>
>Still, I get the following:
>
># explain select * from cam where misscnt>=1;
>NOTICE:  QUERY PLAN:
>
>Seq Scan on cam  (cost=0.00..3609.59 rows=46896 width=66)
>
>Why do postgre think it will get over 46k rows from this query? If I try a
>VACUUM ANALYZE on the table, I get:
>
># explain select * from cam where misscnt>=1;
>NOTICE:  QUERY PLAN:
>
>Seq Scan on cam  (cost=0.00..3874.01 rows=50347 width=66)
>
>So now it actually thinks it will get _more_ rows:
>
># select count(*) from cam where misscnt>=1;
>  count
>-------
>    692
>
>If I use "set enable_seqscan=false;" and try "select * from cam where
>misscnt>=1;" the index is used, and the query executes quite a bit faster.
>However, shouldn't Postgre be able to do this automatically?
>
>This is using PostgreSQL 7.1.2.
>
>
>Thanks.
>
>---
>Kristian Eide
>
>
>
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-- 
Chris Ruprecht
Network grunt and bit pusher extraordinaíre

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