combine multiple row values in to one row

Hi;

I'm looking for a way to do this:


# \d tbl
      Table "public.tbl"
 Column |  Type   | Modifiers
--------+---------+-----------
 idn    | integer |
 code   | text    |
# SELECT * FROM tbl;
 idn | code
-----+------
   1 | A
   2 | B
   2 | C
   3 | A
   3 | C
   3 | E
(6 rows)
# select idn, magic() as codes FROM tbl;
 idn | codes
-----+------
   1 | A
   2 | B, C
   3 | A, C, E
(3 rows)


Right now, I use plpgsql functions, but each time I do it
I have to rewrite the function to customize it.

Is there a generic way to do this? An aggregate maybe?


Thanks for any help.


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