数据库MySQL练习

创建数据表grade：

CREATE TABLE grade(
id INT NOT NULL,
sex CHAR(1),
firstname VARCHAR(20) NOT NULL,
lastname VARCHAR(20) NOT NULL,
english FLOAT,
math FLOAT,
chinese FLOAT
);

向数据表grade中插入几条数据：

INSERT INTO grade
VALUES (1,‘m’,‘John’,‘Smith’,88.0,85.0,82.0),
(2,‘f’,‘Adam’,‘Smith’,76.0,78.0,90.0),
(3,‘m’,‘Allen’,‘William’,88.0,92.0,95.0),
(4,‘m’,‘George’,‘William’,62.0,58.0,72.0),
(5,‘f’,‘Alice’,‘Davis’,89.0,94.0,98.0),
(6,‘m’,‘Kevin’,‘Miller’,77.0,88.0,99.0),
(7,‘f’,‘Helen’,‘Davis’,79.0,83.0,91.0),
(8,‘m’,‘Andrew’,‘Johnson’,81.0,86.0,88.0);

目的：
1、查询所有字段

mysql> select * from grade;

2、查询grade表中的id,firstname,lastname字段

mysql> select id,firstname,lastname from grade;

3、查询grade表中id大于4的学生姓名

mysql> select firstname,lastname from grade
    -> where id<4;

4、查询grade表中女生的记录

mysql> select * from grade
    -> where sex='f';

5、查询grade表中id值为2,4,6的学生记录

mysql> select * from grade
    -> where id in(2,4,6);

6、查询grade表中math成绩在85到94之间的记录

mysql> select * from grade
    -> where math between 85 and 94;

7、查询grade表中firstname以A开头的记录

mysql> select * from grade
    -> where firstname like 'A%';

8、查询grade表中firstname以A开头以e结尾的记录

mysql> select * from grade
    -> where firstname like 'A%' and firstname like '%e';

9、查询grade表中firstname包含l的记录

mysql> select * from grade
    -> where firstname like '%I%';

10、查询grade表中firstname以A开头后面有4个字符的记录

mysql> select * from grade
    -> where firstname like 'A____';

11、查询grade表中english在80到90之间的记录

mysql> select * from grade
    -> where english between 80 and 90;

12、查询grade表中math大于90 或者 chinese大于90的记录

mysql> select * from grade
    -> where math>90 or chinese>90;

13、查询grade表中id不是1、3、5、7的记录

mysql> select * from grade
    -> where id not in(1,3,5,7);

14、查询grade表中的性别有哪些

mysql> select distinct sex from grade;

15、查询grade表中的lastname有哪几种

mysql> select distinct lastname from grade;

16、求出表中所有记录的条数

mysql> select count(*) from grade;

17、求出表中英语成绩的80的记录的条数

mysql> select count(*) from grade
    -> where english=80;

18、计算所有学生的数学成绩的和

mysql> select sum(math) from grade;

19、计算女生的数学成绩的和

mysql> select sum(math) from grade
    -> where sex='f';

20、计算英语成绩平均分

mysql> select avg(english) from grade;

21、计算男生的英语成绩平均分

mysql> select avg(english) from grade
    -> where sex='m';

22、求出数学成绩的最高分

mysql> select max(math) from grade;

23、求出男生中的数学最高分

mysql> select max(math) from grade
    -> where sex='m';

24、按照math成绩的升序进行排列

mysql> select * from grade
    -> order by math asc;

25、按照sex字段的升序和chinese字段的降序排列

mysql> select * from grade
    -> order by sex asc, chinese desc;

26、查询数据表grade中的记录，按照sex字段进行分组

mysql> select count(*) from grade
    -> group by sex;

27、将grade表按照lastname字段值分组，并计算每个分组中的学生数

mysql> select lastname,count(*) from grade
    -> group by lastname
    -> ;

28、对grade表按照lastname字段分组，查出math字段和小于100的组

mysql> select lastname,sum(math) from grade
    -> group by lastname
    -> having sum(math)<100;

29、查询grade表中的第3到第6条记录

mysql> select * from grade limit 2,4;

30、查询grade表中男生平均成绩(三科)大于85的记录

mysql> select * from grade
    -> where sex='m' and (math+chinese+english)/3>85;