On Wed, Aug 4, 2010 at 11:29 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> Oh, yeah. =A0I guess you need this:
>
>> select thing, string_agg(stuff, ',' order by stuff) from agg_test
>> group by thing;
>
>> Rather than this:
>
>> select thing, string_agg(stuff order by stuff, ',') from agg_test
>> group by thing;
>
>> It's all kinds of not obvious to me what the second one is supposed to
>> mean, but I remember this was discussed before. =A0Perhaps we need a
>> <note> somewhere about multi-argument aggregates.
>
> Done:
>
> + =A0 =A0<para>
> + =A0 =A0 When dealing with multiple-argument aggregate functions, note t=
hat the
> + =A0 =A0 <literal>ORDER BY</> clause goes after all the aggregate argume=
nts.
> + =A0 =A0 For example, this:
> + <programlisting>
> + SELECT string_agg(a, ',' ORDER BY a) FROM table;
> + </programlisting>
> + =A0 =A0 not this:
> + <programlisting>
> + SELECT string_agg(a ORDER BY a, ',') FROM table; =A0-- not what you want
> + </programlisting>
> + =A0 =A0 The latter syntax will be accepted, but <literal>','</> will be
> + =A0 =A0 treated as a (useless) sort key.
> + =A0 =A0</para>
Oh, right, that's what it's supposed to mean. Thanks for adding this.
I suppose this confusion is only possible because string_agg has both
a one-argument and a two-argument form.
--=20
Robert Haas
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