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';