Merlin Moncure <mmonc...@gmail.com> writes:
> On Sun, Apr 9, 2017 at 4:27 PM, Guyren Howe <guy...@gmail.com> wrote:
>> If I do a SELECT with a GROUP_BY and multiple ARRAY_AGGs, will the
>> ARRAY_AGGs be guaranteed to have entries in the same (ie corresponding)
>> order?
>>
>> eg
>>
>> SELECT
>> u.name,
>> ARRAY_AGG(o.order_date) AS order_dates,
>> ARRAY_AGG(o.order_total) AS order_totals
>> FROM
>> user u JOIN
>> orders o USING (user_id)
>> GROUP BY
>> u.user_id
> It is unsafe to rely on aggregation order unless specified -- you can
> add ORDER BY to the aggregation clause.
You definitely can't assume anything about the order in which the FROM
clause will deliver rows, but I think that's not quite what the question
was. If I read it right, the OP wants to be sure that the two aggregate
functions will see the data in the *same* unspecified order. I think
that's a pretty safe assumption. The server would have to go way
out of its way to do differently, and it doesn't.
regards, tom lane
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