一、案例（接上一篇文章）

        09）查询学过「张三」老师授课的同学的信息

-- 一共有两种方式
-- 第一种方式：
SELECT s.*,c.cname,t.tname,sc.score 
FROM
	t_mysql_teacher t,
	t_mysql_course c,
	t_mysql_student s,
	t_mysql_score sc
WHERE
	t.tid = c.tid
	and c.cid = sc.cid
	and sc.sid = s.sid
	and t.tname = '张三'
-- 	第二种方式：
-- select * from t_mysql_student where sid in(
-- select sid from t_mysql_score where cid=(select cid from t_mysql_course where tid=
-- (select tid  from t_mysql_teacher where tname='张三')))

        10）查询没有学全所有课程的同学的信息 

SELECT
	s.sid,s.sname,count(sc.score) n
FROM
	t_mysql_student s LEFT JOIN 
	t_mysql_score sc ON s.sid = sc.sid
GROUP BY s.sid,s.sname
HAVING n < (SELECT count(*) from t_mysql_course) 

        11）查询没学过"张三"老师讲授的任一门课程的学生姓名

SELECT
	s.sid,s.sname 
FROM
	t_mysql_score sc,t_mysql_student s 
WHERE
	s.sid = sc.sid 
	AND sc.cid NOT IN ( SELECT cid FROM t_mysql_course c, t_mysql_teacher t WHERE c.tid = t.tid AND t.tname = '张三' ) 
GROUP BY
	s.sid,s.sname

        12）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
	s.sid,s.sname,ROUND(avg( sc.score ),2) 平均成绩
FROM
	t_mysql_student s,t_mysql_score sc 
WHERE
	s.sid = sc.sid and sc.score < 60
GROUP BY
	s.sid,s.sname

         13）检索" 01 "课程分数小于 60，按分数降序排列的学生信息

SELECT
	s.*,sc.cid,sc.score 分数
FROM
	t_mysql_score sc,t_mysql_student s 
WHERE
	s.sid = sc.sid AND sc.cid = '01' AND score < 60 
ORDER BY
	sc.score DESC 

        14）按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

SELECT
	s.sid,s.sname,
	sum((CASE WHEN sc.cid='01' THEN sc.score END)) 语文,
	sum((CASE WHEN sc.cid='02' THEN sc.score END)) 数学,
	sum((CASE WHEN sc.cid='03' THEN sc.score END)) 英语,
	ROUND(avg(sc.score),2) 平均成绩
FROM
	t_mysql_score sc RIGHT JOIN t_mysql_student s 
	ON sc.sid = s.sid 
GROUP BY
	s.sid,s.sname

15）查询各科成绩最高分、最低分和平均分：
以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列 

SELECT
	c.cid,c.cname,count(sc.sid) 人数,
	max(sc.score) 最高分,
	min(sc.score) 最低分,
	ROUND(avg(sc.score),2) 平均分,
	CONCAT(ROUND(sum(if(sc.score>=60,1,0))/(SELECT count(1) from t_mysql_student)*100,2),'%') 及格率,
	CONCAT(ROUND(sum(if(sc.score>=70 and sc.score<80,1,0))/(SELECT count(1) from t_mysql_student)*100,2),'%') 中等率,
	CONCAT(ROUND(sum(if(sc.score>=80 and sc.score<90,1,0))/(SELECT count(1) from t_mysql_student)*100,2),'%') 优良率,
	CONCAT(ROUND(sum(if(sc.score>=90,1,0))/(SELECT count(1) from t_mysql_student)*100,2),'%') 优秀率
FROM
	t_mysql_score sc LEFT JOIN t_mysql_course c
	ON sc.cid = c.cid
GROUP BY c.cid,c.cname

二、思维导图