Re: is there a way to deliver an array over column from a query window? - Mailing list pgsql-general

W dniu 03/24/2013 12:06 PM, Misa Simic pisze:

maybe,

SELECT DISTINCT issuer,amount, array_agg(REFERENCE) over (partition by invoice_nr) from invoices;

RIGHT. Thenx. (and the first thing I did, I've read the doc on array_agg().... what stress makes from people :(

Actually, I have a problem with that (which I haven't noticed earlier because the data I'm having, don't have to many "duplicates" that cause it). The problem is, that:
--------------------------------------
SELECT DISTINCT a, b, c, array_agg(k.d) OVER (PARTITION BY k.c )  FROM testy k where k.e <> 'email' and k.c='1035049' ;
  a   |    b     |    c    |           array_agg          
------+----------+---------+-------------------------------
 1035 | 10410053 | 1035049 | {9902031328529,5951948640868}
---------------------------------------

is _almost_ fine. But I actually need to have control over the order in which the array gathered its values. So I try:
------------------------------------
SELECT DISTINCT a, b, c, array_agg(k.d) OVER (PARTITION BY k.c ORDER BY k.e)  FROM testy k where k.e <> 'email' and k.c='1035049' ;
  a   |    b     |    c    |           array_agg          
------+----------+---------+-------------------------------
 1035 | 10410053 | 1035049 | {5951948640868}
 1035 | 10410053 | 1035049 | {5951948640868,9902031328529}
(2 rows)
--------------------------------------

And this is not at all what I've expected - the aggerate function returned different values over the selected partition.

I understand, that this behavior (of changing the aggregate function return values) is there for the purpose of having sum() - and the like - aggregate functions return accumulating/averaged/etc values as of the example in postgres documentation ( http://www.postgresql.org/docs/9.1/static/tutorial-window.html)

But the array_agg() is significantly different from other aggregate functions - it maintains all the trasspassed values within; under such circumstances: is it reasonable to copy that functionality (of PARTITION OVER ... ORDER BY...) in it?
A particular value relevant to a particular row (when SELECT withiout DISTINCT) can be retrieved by RANK() function used as an index into the resulting array.

But, if (unfortunately) this functionality have to stay: Can somebody pls help me cooking an SQL that returns the same value of array_agg() over the entire partition, while letting me control the order of aggregated values, based on the order of column "E"?

My table for the showcase was:
-----------------------------------
SELECT * FROM testy;
  a   |    b     |    c    |          d           |   e  
------+----------+---------+----------------------+-------
 1035 | 10410053 | 1035049 | 9902031328529        | tel
 1035 | 10410053 | 1035049 | 5291286807@gmail.com | email
 1035 | 10410053 | 1035049 | 5951948640868        | tel2
(3 rows)
------------------------------------------

thx

-R