It is more complex in Postgres, but there is a way with polymorphic types:
CREATE OR REPLACE FUNCTION f_data_of(_tbl_type anyelement)
RETURNS SETOF anyelement AS
$func$
BEGIN
RETURN QUERY EXECUTE 'SELECT * FROM ' || pg_typeof(_tbl_type);
END
$func$ LANGUAGE plpgsql;
Call (important!):
SELECT * FROM f_data_of(NULL::"MyTable");
Detailed explanation in this related answer (see last paragraph: Various complete table types):