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 |

+---------+----------+