drop view assign_v;
create view assign_v as
	select e.code as 番号, e.name as 名前, s.name as 教科, t.name as 講師
		from subject s
		cross join educand e
		left join assign a on (s.code, e.code) = (a.s_code, a.e_code)
		left join teacher t on t.code = a.t_code
		order by e.code, s.code
;