Re: [PERFORM] select max(id) from aTable is very slow

[David Teran]

Hi Nick,

Try using:

SELECT id FROM theTable ORDER BY is DESC LIMIT 1;

Using COUNT, MAX, MIN and any aggregate function on the table of that 
size will always result in a sequential scan. There is currently no 
way around it although there are a few work arounds. See the 
following for more information.

http://archives.postgresql.org/pgsql-performance/2004-01/msg00045.php
http://archives.postgresql.org/pgsql-performance/2004-01/msg00054.php
http://archives.postgresql.org/pgsql-performance/2004-01/msg00059.php

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thanks, that works fine! I will read the mail archive before asking 
such things again ;-)

cheers David

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TIP 9: the planner will ignore your desire to choose an index scan if your
     joining column's datatypes do not match