From: | Enrico Pirozzi <sscotty71(at)gmail(dot)com> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Index scan vs indexonly scan method |
Date: | 2014-10-22 15:18:03 |
Message-ID: | 5447CAAB.7040407@gmail.com |
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Thread: | |
Lists: | pgsql-general |
Hi,
I was working on this simple query
select field1 from table A
where A.field2 <= some_value
order by 1 desc limit some_value
and I saw that:
1) the planner on this query uses an index only scan method:
select field1 from table A
where A.field2 <= '2014-08-13 10:20:59.99648+02'
order by 1 desc limit 100
2) the planner on this query uses a classic index scan method:
select field1 from table A
where A.field2 <= '2014-08-13 10:20:59.99648+02'
order by 1 desc limit 1
the only difference between the two queries is the limit clause,
for the first query the limit is 100 and for the second the limit is 1
it seems a little bit strange...someone can help me to understand why?
My develop PostgreSQL version is a 9.4 beta
regards,
Enrico
--
That's one small step for man; one giant leap for mankind
Enrico Pirozzi
Tel. +39 0861 1855771 - Mob.+39 328 4164437 - Fax +39 0861 1850310
http://www.pgtraining.com <http://www.pgtraining.com-> -
info(at)pgtraining(dot)com
www.enricopirozzi.info - info(at)enricopirozzi(dot)info
PEC: enrico(dot)pirozzi(at)pec(dot)it
Skype sscotty71 - Gtalk sscotty71(at)gmail(dot)com
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