aggregates

Hi,

    I was wonder if anyone has every done this before or if it is at all possible.
I have 3 tables formats,tree,items.  The table creation are shown below.  The values in
the table are also displayed.


CREATE TABLE formats (
    type int4,
    agregatename text
);

CREATE TABLE tree (
    l1 char16,
    l2 char16,
    l3 char16,
    l4 char16,
    l5 char16,
    ident int4,
    type int4
);

CREATE TABLE items (
    ident int4,
    name text ,
    address text,
    email text,
    url text,
    title
);

INSERT INTO FORMATS VALUES(1,'name,email,url');
INSERT INTO TREE VALUES('level1','level2','level3',509,1);
INSERT INTO ITEMS VALUES(28,'foobar','1230 Xmarks Rd', 'foo@bar.com','http://www.perl.pl');


I would like to get the results from ITEMS using returned results from FORMATS as ITEMS'
aggregate to prepare my select query.

I have tried to create a function:

CREATE FUNCTION displayformat(int4)
   RETURNS text
   AS 'select formats from formats where type= $1'
   LANGUAGE  'sql';

and then do the below query:

SELECT displayformat(1) from ITEMS WHERE id=0028;

I get the below result:

displayformat
--------------
name,email,url
(1 row)

Welp! .. I wanted those results returned to me to be seen as aggregates that I would like to
select from ITEMS;

Is it possible to accomplish something like this? Maybe even in a different matter. I just thought
it would be good if I could have a way to set some sort of rule that states what aggregates I need
from the specified query in a table. Is this possible or do I need to somehow keep track of them
seperately (probably causing for the need of a separate query).

Thanks a lot.

-- Thanh