drop table table70;
create table table70 (
id        INTEGER,
query     INTEGER,
checksum  char(2),
score     INTEGER
);
insert into table70 values (1, 1, 'aa',10);
insert into table70 values (2, 2, 'bb',14);
insert into table70 values (3, 3, 'cc',11);
insert into table70 values (4, 1, 'bb',13);
insert into table70 values (5, 2, 'cc',11);
insert into table70 values (6, 3, 'aa',13);
insert into table70 values (7, 1, 'cc',12);
insert into table70 values (8, 2, 'aa',12);
insert into table70 values (9, 3, 'bb',11);

insert into table70 values (11, 1, 'bb',10);
insert into table70 values (12, 2, 'cc',11);
insert into table70 values (13, 3, 'aa',13);
insert into table70 values (14, 1, 'cc',14);
insert into table70 values (15, 2, 'aa',11);
insert into table70 values (16, 3, 'bb',13);
insert into table70 values (17, 1, 'aa',12);
insert into table70 values (18, 2, 'bb',11);
insert into table70 values (19, 3, 'cc',12);

CREATE TYPE topscores AS
	(id integer, query integer, checksum char(2), score integer);

CREATE OR REPLACE FUNCTION topscores(integer) RETURNS SETOF topscores AS 
'
DECLARE
	t topscores%ROWTYPE;
	r RECORD;
	q RECORD;
	i integer;
	n alias for $1;
BEGIN
	FOR q IN SELECT distinct query from table70 order by query LOOP
		i := 0;
		FOR t IN SELECT id , query, checksum, score
			FROM table70
			where query = q.query
			ORDER BY query, score DESC LOOP

			i := i + 1;
			IF i <= n THEN
				RETURN NEXT t;
			ELSE
				EXIT;
			END IF;

		END LOOP;
	END LOOP;
	RETURN;
END;
' language 'plpgsql';

select * from topscores(1) ;
select * from topscores(2) ;
select * from topscores(3) ;

--
-- alternate version using limit rather than count for N
--
CREATE TYPE topscores AS
   (id integer, query integer, checksum char(2), score integer);

CREATE OR REPLACE FUNCTION topscores(integer) RETURNS SETOF topscores AS
'
DECLARE
   t topscores%ROWTYPE;
   r RECORD;
   q RECORD;
   n alias for $1;
BEGIN
   FOR q IN SELECT distinct query from table70 order by query LOOP
      FOR t IN SELECT id , query, checksum, score
         FROM table70
         where query = q.query
         ORDER BY query, score DESC LIMIT n LOOP
            RETURN NEXT t;
      END LOOP;
   END LOOP;
   RETURN;
END;
' language 'plpgsql';