WHAT I did wrong? thank you... :-)

create function test(integer) returns integer as '
   DECLARE
        key ALIAS FOR $1;
        table_data entity%ROWTYPE;
   BEGIN
        INSERT INTO mv_name (ent_id, ent_eid, ent_des)
       select ent_id, ent_eid, ent_des from entity limit 100
       return 1;
end;
' LANGUAGE 'plpgsql';