plpgsql functions

Hi,
I am getting an error for a function written in plpgsql, as -

CREATE OR REPLACE FUNCTION uf_accgroupbal(date, date, p_company integer)
RETURNS SETOF uf_closingbal AS
$BODY$begin
select accgroups."accgroupid", COALESCE(sum(osc),0) as obc,
COALESCE(sum(osd),0) as obd, COALESCE(sum(csc),0) as sc,
COALESCE(sum(csd),0) as sd, (COALESCE(sum(osc),0)+COALESCE(sum(csc),0)) as
cc, (COALESCE(sum(osd),0)+COALESCE(sum(csd),0)) as cd,
accgroups."localglobal", accgroups."companyid", accgroups."isledgeraccount",
accgroups."accgrouplevel", accgroups."mastergroup", accgroups."accobjectid",
accgroups."accobjecttype", accgroups."againstid" from (accgroups left join
(select * from uf_accgroupob($1)) as accob on
accgroups."accgroupid"=accob."accgroupid") left join (select * from
uf_accgroupcurrentbal($1, $2)) as accgcb2 on accgroups."accgroupid" =
accgcb2."accgroupid" group by accgroups."accgroupid",
accgroups."localglobal", accgroups."companyid", accgroups."isledgeraccount",
accgroups."accgrouplevel", accgroups."mastergroup", accgroups."accobjectid",
accgroups."accobjecttype", accgroups."againstid";
end;
$BODY$
LANGUAGE 'plpgsql' VOLATILE
COST 100
ROWS 1000;
giving me an error when called from another function as 'query has no
destination for result data'.
Why? Please give the details about creating functions having only SELECT
statements using plpgsql?, What points to be remembered?

Thanks
CPK