有三张表，学生表，选修课表，学生-选修课表，想查询至少未选修A和B两门课程的学生编号，SQL怎么写，各位大大帮忙看看，谢谢。
建表插数据的语句贴上。
create table Student
(
sid number(8) primary key,
sname varchar2(16),
sex number(8),
age number(8)
);
create table Course
(
cid number(8) primary key,
cname varchar2(16)
);
create table Stu_Course
(
sid number(8),
cid number(8),
primary key(sid,cid)
);
create sequence seq_stu
minvalue 0
start with 0
increment by 1;
create sequence seq_cou
minvalue 0
start with 0
increment by 1;
insert into Student values(seq_stu.nextval,'张三丰',0,24);
insert into Student values(seq_stu.nextval,'梅超风',1,25);
insert into Student values(seq_stu.nextval,'张无忌',0,23);
insert into Student values(seq_stu.nextval,'周芷若',1,22);
insert into Student values(seq_stu.nextval,'柳乘风',0,27);
insert into Student values(seq_stu.nextval,'黄药师',0,18);
insert into Student values(seq_stu.nextval,'周伯通',0,19);
insert into Course values(seq_cou.nextval,'A');
insert into Course values(seq_cou.nextval,'B');
insert into Course values(seq_cou.nextval,'C');
insert into Course values(seq_cou.nextval,'E');
insert into Course values(seq_cou.nextval,'F');
insert into Course values(seq_cou.nextval,'G');
insert into Course values(seq_cou.nextval,'H');
insert into Stu_Course values(1,1);
insert into Stu_Course values(1,2);
insert into Stu_Course values(1,3);
insert into Stu_Course values(2,1);
insert into Stu_Course values(2,2);
insert into Stu_Course values(3,1);
insert into Stu_Course values(3,3);
insert into Stu_Course values(4,1);
insert into Stu_Course values(4,2);
insert into Stu_Course values(4,4);
insert into Stu_Course values(5,1);
insert into Stu_Course values(5,5);
insert into Stu_Course values(5,7);
insert into Stu_Course values(7,1);
