W dniu 04/26/2013 09:54 PM, Misa Simic pisze:
SELECT DISTINCT a, b, c, array_agg(d) OVER (PARTITION BY c ) FROM
(
SELECT a, b, c, d FROM testy where e <> 'email' and c='1035049' ORDER BY a, b, c, e
) t
Doesnt give u desired result?
Hmm... actualy, it looks like it does. I wouldn't thought, that the sort order is maintaned from subquery, but if it does, this is just it.
It looks like I've just overdone the solution.
-R
On Friday, April 26, 2013, Rafał Pietrak wrote:
W dniu 04/26/2013 05:25 PM, Tom Lane pisze:
Rafał Pietrak <rafal@ztk-rp.eu> writes:
array_agg(distinct v order by v) -- works in postgres, but actually I need:
array_agg(distinct v order by v,x) -- which doesn't. (ERROR:
....expressions must appear in argument list),
Why do you think you need that? AFAICS, the extra order-by column could
not in any way affect the result of the operation.
In my particular case (e.g. not in general, since I assume, we all agree, that people do sort things comming out of the query for one purpose or another), is that:
1. the information i retrieve (the V), is a telephone number.
2. my database does keep numerous contact information (e.g. telephone numbers, email, etc) for "entities" registered here - e.g people/companies leave contact information of various relevance: my-private, my-office, my-lawyer, etc.
3. when I need to get in touch with somebody, I need to choose the number that is "most relevant" - one person leaves "my-private" phone, and "my-lawyer" phone; the other leaves "my-office", and "my-lawyer".
4. in the above example I'd like to peek: "my-private" for the first person, and "my-office" for the other. I wouldn't like to relay on randomness provided by the database query plan.
5. so I have "the other" column (the X, e.g "my-something"), that I'd like to sort the array elements by. And peek just the first element of the array.
BTW: I've just rid off the array, and cooked a plain table join with "distinct on ()", which gives just what I needed. My initial plan of using array was to reduce the intermediate row-sets as much as possible as early as possible. Yet, in this case, plain old RDB joins proved to be better (may be not faster - a big multitable join is formed along the query, but conceptually cleaner, which works for me, the database isn't terribly big).
So I have my problem solved, although I haven't figured out a way to have controll over the sort order of array_agg() result - which might be otherwise usefull.
thnx,
-R
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