表：
student
house
course 关系：student_course 多对多
student house 多对一 需求：查询房间1 的学生 都学习了什么课程 select s.s_name,c.c_name from student s
left outer join student_course sc on (s.sid=sc.sid)
left outer join house h on (s.hid=h.hid)
left outer join course c on (sc.cid=c.cid)
where s.sid in (select sid from student) and h.hid=; +---------+----------+
| s_name | c_name |
+---------+----------+
| freedom | odijfoij |
| freedom | in2 |
| wer | odijfoij |
+---------+----------+