1.创建一个库school

create database school

2.在school库中创建class表，有id和name两个字段，要求id字段为主键并且自增，name字段为enum类型，有yun和java两个选项

MariaDB [(none)]> create table school.class

-> (id int primary key auto_increment,

-> name enum ('yun','java'));

Query OK, 0 rows affected (0.03 sec)

3.在class表中和插入2条记录

MariaDB [(none)]> insert into school.class (name) values ('yun'),('java');

4.在school库中创建students表，有s_id,num,name,sex,in_date几个字段，sex设置默认值为m，in_date为入学日期，选者合适的约束，当class表的id字段被修改或删除是，students表中的s_id也跟着改变。

MariaDB [(none)]> create table school.students (

-> s_id int,

-> num int,

-> name char(10),

-> sex enum('m','f') default 'm',

-> in_date date,

-> foreign key (s_id) references school.class (id) on delete cascade on update cascade);

5.在students表中插入5条数据

MariaDB [(none)]> insert into school.students values

-> (1,1,'jim','f','20170215'),

-> (2,2,'tom','f','20170310'),

-> (1,3,'rose','m','20170316'),

-> (1,4,'jack','f','20161008'),

-> (2,5,'xiao','f','20170310');

Query OK, 5 rows affected (0.00 sec)

Records: 5 Duplicates: 0 Warnings: 0

6.查询yun和java班各有多少个学生

MariaDB [(none)]> select s_id,count(s_id) from school.students group by s_id;

+------+-------------+

| s_id | count(s_id) |

+------+-------------+

| 1 | 3 |

| 2 | 2 |

+------+-------------+

2 rows in set (0.00 sec)

MariaDB [(none)]> select in_date,count(in_date) from school.students group by in_date;

+------------+----------------+

| in_date | count(in_date) |

+------------+----------------+

| 2016-10-08 | 1 |

| 2017-02-15 | 1 |

| 2017-03-10 | 2 |

| 2017-03-16 | 1 |

+------------+----------------+

4 rows in set (0.00 sec)