Robert Haas <robertmhaas@gmail.com> writes:
> Oh, yeah. I 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. Perhaps we need a
> <note> somewhere about multi-argument aggregates.
Done:
+ <para>
+ When dealing with multiple-argument aggregate functions, note that the
+ <literal>ORDER BY</> clause goes after all the aggregate arguments.
+ For example, this:
+ <programlisting>
+ SELECT string_agg(a, ',' ORDER BY a) FROM table;
+ </programlisting>
+ not this:
+ <programlisting>
+ SELECT string_agg(a ORDER BY a, ',') FROM table; -- not what you want
+ </programlisting>
+ The latter syntax will be accepted, but <literal>','</> will be
+ treated as a (useless) sort key.
+ </para>
regards, tom lane
