Student(Sid,Sname,Sage,Ssex) 学生表
Course(Cid,Cname,Tid) 课程表
SC(Sid,Cid,score) 成绩表
Teacher(Tid,Tname) 教师表
1、查询“001”课程比“002”课程成绩高的所有学生的学号；
select a.sid from (select sid,score from sc where cid=‘001‘) a
join (select sid,socre from sc where cid=‘002‘) b on a.sid = b.sid
where a.score > b.score;
2 查询平均成绩大于60分的同学的学号和平均成绩；
select sid,avg(score) from sc group by sid having avg(score)>60;
3 查询所有同学的学号、姓名、选课数、总成绩；
select stu.sid,stu.sname,count(cid),sum(score) from student stu join sc s on stu.sid = s.sid
4 查询姓“李”的老师的个数；
select count(tid) from teacher where tname like ‘李%‘;
5 查询没学过“叶平”老师课的同学的学号、姓名；
--叶平老师所带的课程编号 select cid from course where tid = (select tid from teacher where tname="叶平"); ---选过叶平老师课程的学生编号(重要) select distinct sid from sc where cid in (select cid from course where tid = (select tid from teacher where tname="叶平")); ---没有选过叶平老师课程的学生 select sid,sname from student where sid not in (select distinct sid from sc where cid in (select cid from course where tid = (select tid from teacher where tname="叶平")));
6 查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；
--学过“001”--- select sid from sc cid =‘001‘; --学过“002”--- select sid from sc cid =‘002‘; --学过‘001‘同时学过‘002‘(重要 intersect)--- select sid,sname from student where sid in ((select sid from sc cid =‘001‘) intersect (select sid from sc cid =‘002‘)); --- exists
