Postgres8: subselect and optimizer/planner - Mailing list pgsql-general

Hi,

I am fairly new to EXPLAIN, butl working on it. ;-)
I have a few slow running queries I am trying to optimize.

First thing I wonder: I sometimes (lazy) add a subselect to queries.
A stupid example to clearify what I mean:

SELECT U.userid, U.username,
(SELECT G.groupname FROM tblgroup WHERE (G.userid=U.userid)) AS ingroup
FROM tbluser WHERE (bla..bla...);

Will this approach be slower than a regular join?

I mean, will this construct 'force' a repetitive query for each result,
or will Postgres8 see my clumpsy construct, and make a join of it
internally?

Or is my question too general and is the answer 'it depends'?

I found a lot of queries I wrote like that in earlier projects, and I
wonder if I should fix them.
Thanks for any insights!

Regards,
Erwin Moller

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Erwin Moller
Darwine BV

Groenendaal 25f
3011 SK Rotterdam
tel 010-2133996
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