From: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
---|---|
To: | Derrick Rice <derrick(dot)rice(at)gmail(dot)com> |
Cc: | "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: select a list of column values directly into an array |
Date: | 2010-07-30 15:50:03 |
Message-ID: | AANLkTi=dua5s9vgXDJX70DPwJo+q09B8U1D8uDp6Z3i2@mail.gmail.com |
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Lists: | pgsql-general |
On Fri, Jul 30, 2010 at 10:34 AM, Derrick Rice <derrick(dot)rice(at)gmail(dot)com> wrote:
> Is it possible to use the ARRAY(select ...) syntax as a substitute for
> array_agg on versions of postgresql that don't have it? (8.2) It works
> simply enough when only selecting a single column, but if I need to group by
> some other column, I'm not clear how I'd go about doing that.
>
> For example, write the following in ARRAY(select...) form.
yup...we've had array() for ages (I think -- see below).
now, you've always been able to do array aggregation in userland --
it's been in the docs as example since I can remember (see here:
http://www.postgresql.org/docs/8.2/static/xaggr.html)
The old school array_accum however is much slower than the newer
array_agg. (which in turn is just a tiny bit slower than array()
discounting grouping effects). So you _definitely_ want to use
array() if you don't require aggregate grouping features in older
postgres versions.
hm. I looked for the documentation for array(select...) to figure out
exactly when it was introduced, couldn't find it. Anyone know
if/where this is documented?
merlin
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