mysql学习：几十条mysql练习语句（2021-05-02更新）

文章问题导向

mysql单表的数据增删改查如何操作？
如何多表联查？
学完这几十条mysql练习，就可以入门了

如果你都有了答案，可以忽略本文章，或去mysql学习导图寻找更多答案

我的目标：让这个鬼东西变得简单，so easy！！！

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学前数据准备：先建5个表，和插入一些数据，用于查询练习

学生表

学号sno
姓名sname
性别ssex
班级class
出生年月sbrithday

create table `student`(
    `sno` varchar(20) primary key,
    `sname` varchar(20) not null,
    `ssex` varchar(10) not null,
    `class` varchar(20),
    `sbirthday` datetime
);

insert into student values('101','大神','男','202001','1988-08-08');
insert into student values('102','李四','男','202002','1988-08-09');
insert into student values('103','王五','女','202001','1988-06-08');
insert into student values('104','秦明','男','202002','1978-06-09');
insert into student values('105','陈锋','女','202003','1948-02-08');

+-----+-------+------+--------+---------------------+
| sno | sname | ssex | class  | sbirthday           |
+-----+-------+------+--------+---------------------+
| 101 | 大神  | 男   | 202001 | 1988-08-08 00:00:00 |
| 102 | 李四  | 男   | 202002 | 1988-08-09 00:00:00 |
| 103 | 王五  | 女   | 202001 | 1988-06-08 00:00:00 |
| 104 | 秦明  | 男   | 202002 | 1978-06-09 00:00:00 |
| 105 | 陈锋  | 女   | 202003 | 1948-02-08 00:00:00 |
+-----+-------+------+--------+---------------------+

教师表

教师编号tno
教师名称tname
教师性别tsex
出生年月日tbrithday
职称prof
所在部门depart

create table `teacher`(
    `tno` varchar(20) primary key,
    `tname` varchar(20) not null,
    `tsex` varchar(20) not null,
    `tbrithday` datetime,
    `prof` varchar(20) not null,
    `depart` varchar(20) not null
);

insert into teacher values('201','陈老师','男','1978-02-03','副教授', '计算机系');
insert into teacher values('202','李老师','女','1968-04-08','讲师', '电子工程系');
insert into teacher values('203','王老师','男','1958-03-18','讲师', '计算机系');
insert into teacher values('204','唐老师','女','1948-05-07','助教', '电子工程系');

+-----+--------+------+---------------------+--------+------------+
| tno | tname  | tsex | tbirthday           | prof   | depart     |
+-----+--------+------+---------------------+--------+------------+
| 201 | 陈老师  | 男   | 1978-02-03 00:00:00 | 副教授  | 计算机系   |
| 202 | 李老师  | 女   | 1968-04-08 00:00:00 | 讲师    | 电子工程系 |
| 203 | 王老师  | 男   | 1958-03-18 00:00:00 | 讲师    | 计算机系   |
| 204 | 唐老师  | 女   | 1948-05-07 00:00:00 | 助教    | 电子工程系 |
+-----+--------+------+---------------------+--------+------------+

课程表

课程号cno
课程名称cname
教师编号tno

create table `course`(
    `cno` varchar(20) primary key,
    `cname` varchar(20) not null,
    `tno` varchar(20) not null,
    foreign key(tno) references teacher(tno)
);

insert into course values('301','计算机导论','201');
insert into course values('302','操作系统','204');
insert into course values('303','数字电路','202');
insert into course values('304','高等数学','203');

+-----+------------+-----+
| cno | cname      | tno |
+-----+------------+-----+
| 301 | 计算机导论  | 201 |
| 302 | 操作系统    | 204 |
| 303 | 数字电路    | 202 |
| 304 | 高等数学    | 203 |
+-----+------------+-----+

成绩表

学生学号sno
课程号cno
成绩degree

create table `score`(
    `sno` varchar(20) not null,
    `cno` varchar(20) not null,
    `degree` decimal,
    foreign key(sno) references student(sno),
    foreign key(cno) references course(cno),
    primary key(sno, cno)
);

insert into score values('101','301','98');
insert into score values('102','302','88');
insert into score values('103','303','68');
insert into score values('104','301','75');
insert into score values('101','304','100');

+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 101 | 301 |     98 |
| 101 | 304 |    100 |
| 102 | 302 |     88 |
| 103 | 303 |     68 |
| 104 | 301 |     75 |
+-----+-----+--------+

成绩等级表

下限low
上限up
评级grade

create table `grade`(
     low int(3),
     up int(3),
     grade char(1)
 )
 
insert into grade values(90,100,'A');
insert into grade values(80,89,'B');
insert into grade values(70,79,'C');
insert into grade values(60,69,'D');
insert into grade values(0,59,'E');

+------+------+-------+
| low  | up   | grade |
+------+------+-------+
|   90 |  100 | A     |
|   80 |   89 | B     |
|   70 |   79 | C     |
|   60 |   69 | D     |
|    0 |   59 | E     |
+------+------+-------+

---

练习：先思考，再看答案（答案在下方）

0.查询202001 和 202002班全体同学的记录

1.查询teacher表depart列的并集

2.查询score表中成绩在60 到 80之间的记录

3.查询score表中成绩为85， 86 或 88的记录

4.查询student表中202001班或性别为女的同学

5.以class降序查询student表的所有记录

6.以cno升序，degree降序查询score表的所有记录

7.查询student表中202001班的学生人数

8.查询score表中的最高分的学生学号和课程号

9.查询score表中每门课的平均成绩

10.查询score表中至少有2名学生选修的课程

11.双表查询：查询所有学生的sname,cno,和degree列

12.三表联查：查询所有学生的sname,cname,和degree列

13.查询202001班学生每门课的平均分

14.查询score表中，选修301课程，并且成绩低于101号同学的301课程成绩的所有同学记录

15.查询score表中，成绩高于101号同学的301课程成绩的所有记录

16.查询和学号为101，103同学同年出生的所有学生的sno,sname,sbirthday列

17.查询'陈老师'任课的学生成绩

18.查询选修课程的同学人数大于5人的教师姓名（只要老师教的课，有超过5人选修，就满足条件）
因为数据不够多，可以改成2，或者自己添加数据

19.查询最高分同学的信息

20.查询所有男教师所教的课程

21.查询选修课程编号为301且成绩至少一个高于选修302课程的同学记录

22.查询出计算机系教师所教课程的成绩表

23.查询所有老师和同学的name, sex, birthday

24.查询所有女教师和女同学的name,sex, birthday

25.查询student中不姓'李'的同学记录

26.查询student中每个学生的姓名和年龄

27.查询student中最大和最小的年龄

28.查询 和'李四' 同性别的所有同学的sname，不要李四

29.查询 和'李四' 同性别的并且同班的所有同学的sname

30.查询所有选修 计算机导论 课程的男同学的成绩表

31.双表查询：查询所有同学的sno, cno, grede列

32.四表联查：查询所有有成绩的同学的名字, 课程, 成绩等级

答案

0. 使用包含条件in
select * from student where class in (202001,202002);
+-----+-------+------+--------+---------------------+
| sno | sname | ssex | class  | sbirthday           |
+-----+-------+------+--------+---------------------+
| 101 | 大神  | 男   | 202001 | 1988-08-08 00:00:00 |
| 102 | 李四  | 男   | 202002 | 1988-08-09 00:00:00 |
| 103 | 王五  | 女   | 202001 | 1988-06-08 00:00:00 |
| 104 | 秦明  | 男   | 202002 | 1978-06-09 00:00:00 |
+-----+-------+------+--------+---------------------+

1. 使用去重distinct
select distinct depart from teacher;
+------------+
| depart     |
+------------+
| 计算机系    |
| 电子工程系  |
+------------+

2.使用条件运算符 或 范围查找
select * from score where degree between 60 and 80;
select * from score where degree > 60 and degree < 80;
+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 103 | 303 |     68 |
| 104 | 301 |     75 |
+-----+-----+--------+

3.使用包含运算符
select * from score where degree in(85, 86, 88);
+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 102 | 302 |     88 |
+-----+-----+--------+

4.使用条件运算符
select * from student where class = '202001' or ssex = '女';
+-----+-------+------+--------+---------------------+
| sno | sname | ssex | class  | sbirthday           |
+-----+-------+------+--------+---------------------+
| 101 | 大神  | 男   | 202001 | 1988-08-08 00:00:00 |
| 103 | 王五  | 女   | 202001 | 1988-06-08 00:00:00 |
| 105 | 陈锋  | 女   | 202003 | 1948-02-08 00:00:00 |
+-----+-------+------+--------+---------------------+

5.使用order by
select * from student order by class desc;
+-----+-------+------+--------+---------------------+
| sno | sname | ssex | class  | sbirthday           |
+-----+-------+------+--------+---------------------+
| 105 | 陈锋  | 女   | 202003 | 1948-02-08 00:00:00 |
| 102 | 李四  | 男   | 202002 | 1988-08-09 00:00:00 |
| 104 | 秦明  | 男   | 202002 | 1978-06-09 00:00:00 |
| 101 | 大神  | 男   | 202001 | 1988-08-08 00:00:00 |
| 103 | 王五  | 女   | 202001 | 1988-06-08 00:00:00 |
+-----+-------+------+--------+---------------------+

6.多个排序
select * from score order by cno asc, degree desc;
+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 101 | 301 |     98 |
| 104 | 301 |     75 |
| 102 | 302 |     88 |
| 103 | 303 |     68 |
| 101 | 304 |    100 |
+-----+-----+--------+

7. 使用函数
select count(*) count from student where class = '202001';
+-------+
| count |
+-------+
|     2 |
+-------+

8.使用条件子句，先找到最高分，再找学生学号和课程号
select sno, cno from score where degree=(select max(degree) from score);
+-----+-----+
| sno | cno |
+-----+-----+
| 101 | 304 |
+-----+-----+

9.以cno分组，再使用avg函数计算平均数
一门课：select cno, avg(degree) avg_degree from score where cno = '301';
每门课：select cno, avg(degree) avg_degree from score group by cno;
+-----+------------+
| cno | avg_degree |
+-----+------------+
| 301 |    86.5000 |
| 302 |    88.0000 |
| 303 |    68.0000 |
| 304 |   100.0000 |
+-----+------------+

10. 先分组，再计算筛选
select cno from score group by cno having count(cno) >= 2;
+-----+
| cno |
+-----+
| 301 |
+-----+

11. from后可以多个表，以，隔开， 或使用内联查询
select sname, cno, degree from student,score where student.sno = score.sno;
或
select sname,cno,degree from student inner join score on student.sno = score.sno;
+-------+-----+--------+
| sname | cno | degree |
+-------+-----+--------+
| 大神  | 301 |     98 |
| 大神  | 304 |    100 |
| 李四  | 302 |     88 |
| 王五  | 303 |     68 |
| 秦明  | 301 |     75 |
+-------+-----+--------+

12.三表联查
select sname, cname, degree from student, course, score where student.sno = score.sno and course.cno = score.cno;
+-------+------------+--------+
| sname | cname      | degree |
+-------+------------+--------+
| 大神  | 计算机导论   |     98 |
| 秦明  | 计算机导论   |     75 |
| 李四  | 操作系统     |     88 |
| 王五  | 数字电路     |     68 |
| 大神  | 高等数学     |    100 |
+-------+------------+--------+

进阶：按sname升序和degree降序，如果需要limit还可以在后面加
select sname, cname, degree from student, course, score where student.sno = score.sno and course.cno = score.cno order by sname asc, degree desc;
+-------+------------+--------+
| sname | cname      | degree |
+-------+------------+--------+
| 大神  | 高等数学    |    100 |
| 大神  | 计算机导论  |     98 |
| 李四  | 操作系统    |     88 |
| 王五  | 数字电路    |     68 |
| 秦明  | 计算机导论  |     75 |
+-------+------------+--------+

13. 原则：复杂的查询，先分段进行
先获取202001班的所有学生学号：select sno from student where class = '202001'；
再获取这些学生的所有课程：select * from score where sno in (select sno from student where class='202001');
最后以课程分组和计算平均分：select cno, avg(degree) avg_drgree from score where sno in (select sno from student where class='202001') group by cno;
+-----+------------+
| cno | avg_drgree |
+-----+------------+
| 301 |    98.0000 |
| 304 |   100.0000 |
| 303 |    68.0000 |
+-----+------------+

14. 使用条件子句
先查询101号同学的301号课程成绩：select degree from score where sno = '101' and cno = '301';
再获取301号课程的其他同学：select * from score where cno = '301' and degree < (select degree from score where sno='101' and cno='301');
+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 104 | 301 |     75 |
+-----+-----+--------+

15. 使用条件子句
select * from score where degree > (select degree from score where sno = '101' and cno = '301');
+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 101 | 304 |    100 |
+-----+-----+--------+

16. 使用year()函数
先获取101，103同学的日期：select year(sbirthday) from student where sno in (101,103);
再获取其他学生：select * from student where year(sbirthday) in (select year(sbirthday) from student where sno in (101,103));
+-----+-------+------+--------+---------------------+
| sno | sname | ssex | class  | sbirthday           |
+-----+-------+------+--------+---------------------+
| 101 | 大神  | 男   | 202001 | 1988-08-08 00:00:00 |
| 102 | 李四  | 男   | 202002 | 1988-08-09 00:00:00 |
| 103 | 王五  | 女   | 202001 | 1988-06-08 00:00:00 |
+-----+-------+------+--------+---------------------+

17. 多层嵌套查询
分析：成绩需要在成绩表里取，但成绩表里不知道陈老师教的是什么课，需要去课程表里取，课程表里不知道陈老师的编号是多少，需要去老师表里取。
先在teacher获取陈老师的编号：select tno from teacher where tname = '陈老师';
再到course获取陈老师的课程编号：select cno from course where tno = (select tno from teacher where tname = '陈老师');
最后根据课程编号获取学生成绩：select * from score where cno = (select cno from course where tno = (select tno from teacher where tname = '陈老师'));
+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 101 | 301 |     98 |
| 104 | 301 |     75 |
+-----+-----+--------+

18. 多层嵌套查询
先获取课程编号，分组，筛选，计算总数：select cno from score group by cno having count(*) >= 2;
再获取老师编号： select tno from course where cno = (select cno from score group by cno having count(*) >= 2);
最后获取老师名字：select * from teacher where tno = (select tno from course where cno=(select cno from score group by cno having count(*) >= 2));
+-----+--------+------+---------------------+--------+----------+
| tno | tname  | tsex | tbirthday           | prof   | depart   |
+-----+--------+------+---------------------+--------+----------+
| 201 | 陈老师  | 男   | 1978-02-03 00:00:00 | 副教授  | 计算机系  |
+-----+--------+------+---------------------+--------+----------+

19. 多层嵌套查询
select * from student where sno = (select sno from score where degree in (select max(degree) from score));
+-----+-------+------+--------+---------------------+
| sno | sname | ssex | class  | sbirthday           |
+-----+-------+------+--------+---------------------+
| 101 | 大神  | 男    | 202001 | 1988-08-08 00:00:00 |
+-----+-------+------+--------+---------------------+

20.
select tno from teacher where tsex = '男';
select * from course where tno in (select tno from teacher where tsex = '男');
+-----+------------+-----+
| cno | cname      | tno |
+-----+------------+-----+
| 301 | 计算机导论  | 201 |
| 304 | 高等数学    | 203 |
+-----+------------+-----+

21. 使用any：任何一个
select * from score where cno = '301';
select * from score where cno = '302' and degree > any(select degree from score where cno='301');
+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 102 | 302 |     88 |
+-----+-----+--------+

22.稍后补上

23. 双表联查：使用as 和 union联表查询
select tname as name, tsex as sex, tbirthday as birthday from teacher union select sname, ssex, sbirthday from student;
+--------+-----+---------------------+
| name   | sex | birthday            |
+--------+-----+---------------------+
| 陈老师 | 男  | 1978-02-03 00:00:00 |
| 李老师 | 女  | 1968-04-08 00:00:00 |
| 王老师 | 男  | 1958-03-18 00:00:00 |
| 唐老师 | 女  | 1948-05-07 00:00:00 |
| 大神   | 男  | 1988-08-08 00:00:00 |
| 李四   | 男  | 1988-08-09 00:00:00 |
| 王五   | 女  | 1988-06-08 00:00:00 |
| 秦明   | 男  | 1978-06-09 00:00:00 |
| 陈锋   | 女  | 1948-02-08 00:00:00 |
+--------+-----+---------------------+

24. 双表联查：union联表查询 + where
select tname as name, tsex as sex, tbirthday as birthday from teacher where tsex = '女' union select sname, ssex, sbirthday from student where ssex = '女';
+--------+-----+---------------------+
| name   | sex | birthday            |
+--------+-----+---------------------+
| 李老师 | 女   | 1968-04-08 00:00:00 |
| 唐老师 | 女   | 1948-05-07 00:00:00 |
| 王五   | 女   | 1988-06-08 00:00:00 |
| 陈锋   | 女   | 1948-02-08 00:00:00 |
+--------+-----+---------------------+

25.使用模糊查询like
select * from student where sname not like '李%';
+-----+-------+------+--------+---------------------+
| sno | sname | ssex | class  | sbirthday           |
+-----+-------+------+--------+---------------------+
| 101 | 大神  | 男   | 202001 | 1988-08-08 00:00:00 |
| 103 | 王五  | 女   | 202001 | 1988-06-08 00:00:00 |
| 104 | 秦明  | 男   | 202002 | 1978-06-09 00:00:00 |
| 105 | 陈锋  | 女   | 202003 | 1948-02-08 00:00:00 |
+-----+-------+------+--------+---------------------+

26.使用now() + year()
年龄：当前年 - 出生年
select year(sbirthday) from student;
select sname, year(now())-year(sbirthday) as 'age' from student;
+-------+------+
| sname | age  |
+-------+------+
| 大神  |   33 |
| 李四  |   33 |
| 王五  |   33 |
| 秦明  |   43 |
| 陈锋  |   73 |
+-------+------+

27. min/max + year + now
注意：时间越多，年龄越小
select year(now())-year(min(sbirthday)) as max_age, year(now())-year(max(sbirthday)) as min_age from student;
+---------+---------+
| max_age | min_age |
+---------+---------+
|      73 |      33 |
+---------+---------+

29. 条件拼接
select sname from student where ssex = (select ssex from student where sname='李四') and sname != '李四';
+-------+
| sname |
+-------+
| 大神  |
| 秦明  |
+-------+

30. 条件拼接
select sname from student where ssex = (select ssex from student where sname='李四') and sname != '李四' and class = (select class from student where sname = '李四');
+-------+
| sname |
+-------+
| 秦明  |
+-------+

30.
select * from student where ssex = '男';
select cno from course where cname = '计算机导论';
select * from score where cno = (select cno from course where cname = '计算机导论') and sno in (select sno from student where ssex = '男');
+-----+-----+--------+
| sno | cno | degree |
+-----+-----+--------+
| 101 | 301 |     98 |
| 104 | 301 |     75 |
+-----+-----+--------+

31.双表查询
select sno, cno, grade from score, grade where degree between low and up;
+-----+-----+-------+
| sno | cno | grade |
+-----+-----+-------+
| 101 | 301 | A     |
| 101 | 304 | A     |
| 102 | 302 | B     |
| 104 | 301 | C     |
| 103 | 303 | D     |
+-----+-----+-------+

32. 四表联查：学生表，成绩表，课程表，成绩等级表，多表，多条件
全部字段：select * from student as stu, score as sco, course as cou, grade as gra where sco.cno = cou.cno and stu.sno = sco.sno and sco.degree between low and up;
要的字段：select stu.sno, sname, cname, grade from student as stu, score as sco, course as cou, grade as gra where sco.cno = cou.cno and stu.sno = sco.sno and sco.degree between low and up;
+-----+-------+------------+-------+
| sno | sname | cname      | grade |
+-----+-------+------------+-------+
| 101 | 大神  | 计算机导论   | A     |
| 101 | 大神  | 高等数学     | A     |
| 102 | 李四  | 操作系统     | B     |
| 103 | 王五  | 数字电路     | D     |
| 104 | 秦明  | 计算机导论   | C     |
+-----+-------+------------+-------+

后补

暂无

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