From: Tom Lane <tgl@sss.pgh.pa.us>
To: jdmorgan <jdmorgan@unca.edu>
Cc: pgsql-sql@postgresql.org
Subject: Re: array_agg order by
Date: Mon, 27 Feb 2012 23:15:37 -0500
Message-ID: <25514.1330402537@sss.pgh.pa.us> (raw)
In-Reply-To: <4F4C4EF4.4000006@gmail.com>
References: <4F4C4EF4.4000006@gmail.com>
jdmorgan <jdmorgan@unca.edu> writes:
> I am using a array_agg to get a subset of data to use in a
> query.However, I can't figure out how to get the data returned in the
> array_agg function to sort with an order by function.Any help would be
> appreciated.Here is my query as it is now.I am using postgresql 8:
Well, if you were using 9.0 or later, you could do this "right":
select array_agg(foo order by bar), otherstuff from ..tables..;
You can kind of get there in older versions with a sub-select:
select array_agg(foo), otherstuff
from
(select foo, otherstuff from ..tables.. order by whatever) ss;
However that's a bit shaky because you can't do very much in the outer
query, like say grouping, without risking messing up the sort ordering.
You have to keep a close eye on the EXPLAIN output for your query to
make sure nothing re-sorts the data before it gets to the Aggregate
step.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, jdmorgan@unca.edu
Subject: Re: array_agg order by
In-Reply-To: <25514.1330402537@sss.pgh.pa.us>
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