回顾MySQL查询经典实例3

#查询姓氏是李的老师的数量

select count(*) as nameNum
from teacher
where tname like '李%';

#查询学习过张三老师课程的学生信息
#多表联合查询

select student.* from student,teacher,course,score
where 
    student.sid = score.sid 
    and course.cid=score.cid 
    and course.tid = teacher.tid 
    and tname = '张三';

#查询没有学习所有课程的同学信息
#因为有学生什么课都没有选，反向思考，先查询选了所有课的学生，再选择这些人之外的学生.

select * from student
where student.sid not in (
  select score.sid from score
  group by score.sid
  having count(score.cid)= (select count(cid) from course)
);

#查询至少有一门课程与学号为“01”的同学所学相同的同学的信息

select * from student 
where student.sid in (
    select score.sid from score 
    where score.cid in(
        select score.cid from score 
        where score.sid = '01'
    )

#查询没有学过张三老师的任一门课的学生姓名
#嵌套查询

select * from student
    where student.sid not in(
        select score.sid from score where score.cid in(
            select course.cid from course where course.tid in(
                select teacher.tid from teacher where tname = "张三"
            )
        )
    );

#查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

select student.sid, student.sname,b.avgScore
from student RIGHT JOIN
(select sid, AVG(score) as avgScore from score
    where sid in (
              select sid from score 
              where score<60 
              GROUP BY sid 
              HAVING count(score)>1)
    GROUP BY sid) b on student.sid=b.sid;

#检索" 01 "课程分数小于 60，按分数降序排列的学生信息

select student.*, score.score from student, score
where student.sid = score.sid
and score.score < 60
and cid = "01"
ORDER BY score.score DESC;