On Nov 7, 2005, at 23:24 , Tom Lane wrote:
Strictly speaking, you need this:
select bar_id, array_accum(foo_value) from
(select * from ordered_foo order by bar_id, foo_pos) as ss
group by bar_id order by bar_id;
ie, sort the subselect by the grouping key of the outer query, then
by the thing that should control the aggregation order within groups.
The way Joe shows will work only if the planner chooses to use a hash
aggregate plan. If it chooses a sort/uniq aggregation plan, the re-
sort
will destroy the sort order of the sub-select's output.
Thanks, Tom. That fixed the problem in the production version. Is the
ability to do this an artifact of the sorting or defined by the SQL?
I.e., can I expect this to work even if the plan changes? I'm
guessing not, but that's just a guess.
Michael Glaesemann
grzm myrealbox com
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