MYSQL思考题八_Mysql 经典50题练习

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工作之后发现自己已经不太会写sql了，除了业务方面的学习，技术上也不能落下啊。于是打算做一遍这50题，通过实际操作来加深对sql的理解。
CREATE TABLE student (
sid varchar(10),
sname varchar(10),
sage datetime,
ssex varchar(10)
);
insert into student values('01' , '赵雷' , '1990-01-01' , '男');
insert into student values('02' , '钱电' , '1990-12-21' , '男');
insert into student values('03' , '孙风' , '1990-05-20' , '男');
insert into student values('04' , '李云' , '1990-08-06' , '男');
insert into student values('05' , '周梅' , '1991-12-01' , '女');
insert into student values('06' , '吴兰' , '1992-03-01' , '女');
insert into student values('07' , '郑竹' , '1989-07-01' , '女');
insert into student values('08' , '王菊' , '1990-01-20' , '女');
CREATE TABLE course (
cid varchar(10),
cname varchar(10),
tid varchar(10)
);
insert into course values('01' , '语文' , '02');
insert into course values('02' , '数学' , '01');
insert into course values('03' , '英语' , '03');
CREATE TABLE teacher (
tid varchar(10),
tname varchar(10)
);
insert into teacher values('01' , '张三');
insert into teacher values('02' , '李四');
insert into teacher values('03' , '王五');
CREATE TABLE sc (
sid varchar(10),
cid varchar(10),
score decimal(18, 1)
);
insert into sc values('01' , '01' , 80);
insert into sc values('01' , '02' , 90);
insert into sc values('01' , '03' , 99);
insert into sc values('02' , '01' , 70);
insert into sc values('02' , '02' , 60);
insert into sc values('02' , '03' , 80);
insert into sc values('03' , '01' , 80);
insert into sc values('03' , '02' , 80);
insert into sc values('03' , '03' , 80);
insert into sc values('04' , '01' , 50);
insert into sc values('04' , '02' , 30);
insert into sc values('04' , '03' , 20);
insert into sc values('05' , '01' , 76);
insert into sc values('05' , '02' , 87);
insert into sc values('06' , '01' , 31);
insert into sc values('06' , '03' , 34);
insert into sc values('07' , '02' , 89);
insert into sc values('07' , '03' , 98);
查询"01"课程比"02"课程成绩高的学生的信息及课程分数
keyword : 自连接(SELF JOIN)
SELECT student.*, sc1.score AS 'course-01', sc2.score AS 'course-02'
FROM student, sc sc1, sc sc2
WHERE student.sid = sc1.sid
AND sc1.sid = sc2.sid
AND sc1.cid = '01'
AND sc2.cid = '02'
AND sc1.score > sc2.score
<img alt="9abffdd334fa" src="https://beijingoptbbs.oss-cn-beijing.aliyuncs.com/cs/5606289-3d795cd176cb29f4bb7cd48bbbee4616">
1.1 查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )
keyword : LEFT JOIN
SELECT *
FROM
( SELECT * FROM sc WHERE sc.cid = '01' ) sc1
LEFT JOIN ( SELECT * FROM sc WHERE sc.cid = '02' ) sc2 ON sc1.sid = sc2.sid
<img alt="9abffdd334fa" src="https://beijingoptbbs.oss-cn-beijing.aliyuncs.com/cs/5606289-3d795cd176cb29f4bb7cd48bbbee4616">
1.2 查询同时存在01和02课程的情况
keyword : 子查询
SELECT *
FROM
( SELECT * FROM sc WHERE sc.cid = '01' ) sc1,
( SELECT * FROM sc WHERE sc.cid = '02' ) sc2
WHERE sc1.sid = sc2.sid
<img alt="9abffdd334fa" src="https://beijingoptbbs.oss-cn-beijing.aliyuncs.com/cs/5606289-3d795cd176cb29f4bb7cd48bbbee4616">
1.3 查询选择了02课程但没有01课程的情况
keyword : NOT IN
SELECT *
FROM sc
WHERE cid = '02' AND sid NOT IN ( SELECT sid FROM sc WHERE cid = '01' )
<img alt="9abffdd334fa" src="https://beijingoptbbs.oss-cn-beijing.aliyuncs.com/cs/5606289-3d795cd176cb29f4bb7cd48bbbee4616">
2.查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩
keyword : GROUP BY、HAVING
--注意版本默认的model问题
SELECT sc.sid,s.sname,avg(score)
FROM student s INNER JOIN sc ON s.sid = sc.sid
GROUP BY sid
HAVING (avg(score) >= 60)
<img alt="9abffdd334fa" src="https://