面试题一SQL语句

面试题一SQL语句

学生表：

Student(sid,sname,sage,ssex) --学生编号，学生姓名，出生日期，学生性别

课程表：

Course(cid,cname,tid) --课程编号，课程名称，教师编号

教师表

Teacher(tid,tname) --教师编号，教师姓名

成绩表

Sc(sid,cid,score) --学生编号，课程编号，分数

SQL语句：

1. 查询“01”课程比“02”课程成绩高的学生的信息及课程分数

   select a.*,b.score,c.score
   from student a
   left join sc b on a.sid=b.sid and b.cid='01'
   left join sc c on a.sid=c.sid and c.cid='02'
   where b.score>c.score
   

2. 查询平均成绩大于等于60分的同学的学生编号，学生姓名和平均成绩

   select a.sid，a.sname，avg(sc.score) avg_score
   from student a,sc
   where a.sid = sc.sid
   group by a.sid,a.sname
   having avg_score>=60
   order by a.sid;
   

3. 查询所有学生的学生编号，学生姓名，选课总数，所有课程订单总成绩

   select a.sid,a.sname,count(b.cid),sum(b.score)
   from student a
   left join sc b
   on a.sid=b.sid
   group by a.sid,a.sname
   order by a.sid
   

4. 统计课程分01最高的前三名学生信息

   select a.sname,sc.score,sc.cid
   from student a
   join sc 
   on a.sid=sc.sid
   where sc.cid='01'
   order by sc.score desc limit 3;
   

5. 统计每个学生的选课总数

   select a.sid,a.sname,count(b.cid)
   from student a
   left join sc b
   on a.sid=b.sid
   group by a.sid,a.sname
   

6. 查询没学过“张三”老师授课的学生信息

   select a.*
   from student a
   left join sc b
   where not exists(
       select *
       from course c
       inner join teacher d
       on c.tid=d.tid
       inner join sc e
       on c.cid=e.cid
       where d.tname='张三'
       and e.sid = a.sid
   )
   group by 1,2,3,4;
   

7. 查询学过编号“01”并且也学过编号“02”的课程的学生信息

   select a.*
   from student a
   inner join sc b
   on a.sid = b.sid and b.cid ='01'
   inner join sc c
   on a.sid = c.sid on c.cid='02';