- 与"李威彤"同乡的男生姓名
SELECT sname,snativeplace FROM student WHERE snativeplace IN
(SELECT snativeplace FROM student WHERE sid IN
(SELECT sid FROM student WHERE ssex='男')
AND sid IN
(SELECT sid FROM student WHERE sname='李威彤')
)
- 选修 ‘刘强’ 老师所讲课程的学生人数
select count(sid) from student where sid in
(select sid from mark where cid in
(select cid from course where tid in
(select tid from teacher where tname='刘强')
)
)
- 统计每门课的平均成绩,并按顺序降序排序
select cname,avg(cmark)amk from mark,course group by cname order by amk desc
待续