Getting one row for each subquery row...? - Mailing list pgsql-general

adding comments to a tableHi All,
here are my three tables. I wold like to list them in the following way: I
need all the columns from t_stockchanges, and one field for the pgoductgroup
the t_stockchanges.productid belongs to.

But one product can belong to many group, so i would need one row for each
group for each product.

My bad query is:
------------------------
DB=# select t_stockchanges.productid, (select name from t_productgroups
where id=(select productgroupid from t_prod_in_pgr where
productid=t_stockchanges.productid)) as pgroup from t_stockchanges;
ERROR:  More than one tuple returned by a subselect used as an expression.
DB=#
---------------
Yes, this is absolutelly true, but I would like postgres to give me all the
tuples found. How can I ask him to do so?

Thank you,
-- Csaba

----------------------------------------------------------------------------
----------------------------------------------------
                             Table "public.t_stockchanges"
    Column     |       Type       |                      Modifiers
---------------+------------------+-----------------------------------------
------------
 id            | integer          | not null
 stockid       | integer          | not null
 productid     | integer          | not null
 changeid      | integer          | not null
 quantity      | double precision | not null
 date          | character(19)    | not null
 purchaseprice | double precision | not null
 correction    | double precision | not null
 userid        | integer          | not null
 time          | character(19)    | default to_char(now(), 'YYYY.mm.dd
hh:mi:ss'::text)
 prooftype     | character(10)    | not null default ''
 proofid       | integer          | default 0
Indexes: t_stockchanges_pkey primary key btree (id),
         t_stockchanges_date btree (date),
         t_stockchanges_productid btree (productid)
----------------------------------------------------------------------------
----------------------------------------------------

         Table "public.t_productgroups"
   Column    |         Type          | Modifiers
-------------+-----------------------+-----------
 id          | integer               | not null
 name        | character varying(30) | not null
 description | character varying     |
 root        | boolean               |
Indexes: t_productgroups_pkey primary key btree (id)
----------------------------------------------------------------------------
----------------------------------------------------

     Table "public.t_prod_in_pgr"
     Column     |  Type   | Modifiers
----------------+---------+-----------
 productgroupid | integer | not null
 productid      | integer | not null
----------------------------------------------------------------------------
----------------------------------------------------


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