01）查询学过「张三」老师授课的同学的信息
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'
02）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( 1 )
FROM
t_mysql_course)
03）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
04）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,
avg( sc.score ) n
FROM
t_mysql_student s,
t_mysql_score sc
WHERE
s.sid = sc.sid
AND sc.score < 60
GROUP BY
s.sid,
s.sname
05）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.score
FROM
t_mysql_student s,
t_mysql_score sc
WHERE
s.sid = sc.sid
AND sc.cid = '01'
AND sc.score < 60
ORDER BY
sc.score DESC
06）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(if(sc.cid = '01',sc.score,0)) 语文,
sum(if(sc.cid = '02',sc.score,0)) 数学,
sum(if(sc.cid = '03',sc.score,0)) 英语,
ROUND(avg(sc.score),2) 平均分
FROM
t_mysql_score sc
RIGHT JOIN t_mysql_student s ON sc.sid = s.sid
GROUP BY
s.sid,
s.sname
07）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
