Re: ordered by join? ranked aggregate? how to?

In response to wstrzalka :
> What I need is to join 2 tables
>
> CREATE TABLE master(
> id INT4
> );
>
>
> CREATE TABLE slave (
> master_id INT4,
> rank INT4,
> value TEXT);
>
>
> What I need is to make the query:
>
> SELECT m.id, array_agg(s.value) AS my_problematic_array
> FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id)
> GROUP BY m.id;
>
> return the 'my_problematic_array' in order specified by slave.rank
>
> As you probably can guest I don't have any idea know how to do it :/

test=*# select * from master;
id
----
1
2
(2 rows)

test=*# select * from slave;
master_id | rank | value
-----------+------+-------
1 | 5 | 5
1 | 3 | 3
1 | 7 | 7
(3 rows)

test=*#
select id, array_agg(unnest) from (
select id, unnest(my_problematic_array) from (
SELECT m.id, array_agg(s.value) AS my_problematic_array FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id) GROUP BY m.id
) foo order by 1,2
) bar group by 1;
id | array_agg
----+-----------
1 | {3,5,7}
2 | {NULL}
(2 rows)

Andreas
--
Andreas Kretschmer
Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: -> Header)