some code that may help:

postgres=# CREATE TABLE myTable (
postgres(# id int,
postgres(# sid int,
postgres(# name text);
CREATE TABLE
postgres=#
postgres=# insert into myTable values(1,2,'a');
INSERT 0 1
postgres=# insert into myTable values(2,3,'b');
INSERT 0 1
postgres=#
postgres=# select * from myTable;
id | sid | name
----+-----+------
1 | 2 | a
2 | 3 | b
(2 rows)

postgres=#
postgres=# CREATE FUNCTION getData(int) RETURNS SETOF myTable AS $$
postgres$# SELECT * FROM myTable WHERE id = $1;
postgres$# $$ LANGUAGE SQL;
CREATE FUNCTION
postgres=#
postgres=# SELECT * FROM getData(1) AS t1;
id | sid | name
----+-----+------
1 | 2 | a
(1 row)

postgres=#
postgres=# drop function getData(int);
DROP FUNCTION
postgres=# drop table myTable;
DROP TABLE
postgres=#