mysql数据库表的管理（2）

一：表的字段类型

在这里插入图片描述

二：表的字段约束

字段约束用来确保数据的完整性（可靠性和准确性）

unique 唯一性约束
值不可重复；
not null 非空约束
值不可为空；
default 默认值约束
当增加数据时没有插⼊值时，会自动插⼊默认值；
primary key 主键约束
主键约束 = 唯一性约束 + 非空约束

是一张表的代表性字段，一张表只能有一个主键。

主键可以是一个字段，也可以是多个字段（联合主键，复合主键）。

整形主键字段可以使用auto_increment（自动增长）修饰，插入时不写主键字段值，值 = 上一列值 + 1；
foreign key 外键约束
外键是另一表的主键，常用来和其他表建立联系。

外键与主键的引用类型必须一致，如果主键是int外键是char则不行。
一定要匹配主表中引用的列 ( 所要创建的外键是主表中的主键 )。
主键和外键的字符编码必须一致，如果主表为utf8，则此表也要为utf8。
auto_increment 自增约束
标识该属性的值会自动增长。
一个表中只能有一个字段使用该约束，而且该字段必须是主键。

三：表的创建、删除

3.1 创建表

create table 表名(
字段名1  类型  [字段约束],
字段名2  类型  [字段约束],
…
);

例子：

mysql> create table s1(id int primary key auto_increment,name varchar(50) not null,sex varchar(10));
Query OK, 0 rows affected (0.09 sec)

3.2 删除表

方法1：drop table 表名;

举例：

显示所有的表
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| s1             |
| s2             |
+----------------+
2 rows in set (0.00 sec)
删除表：S2
mysql> drop table s2;
Query OK, 0 rows affected (0.00 sec)

方法2：drop table if exists 表名;

四：修改表的结构

4.1 查看表结构

desc 表名;

mysql> desc s1;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| name  | varchar(50) | NO   |     | NULL    |                |
| sex   | varchar(10) | YES  |     | 男      |                |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

4.2 修改表结构

4.2.1 增加一列字段

alter table 表名 add 字段名字段类型 [after 列名];

举例：

MariaDB [test]> alter table s2 add sex enum('男','女');
Query OK, 0 rows affected (0.01 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> desc s1;
+-------+---------------+------+-----+---------+-------+
| Field | Type          | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+-------+
| id    | int(11)       | YES  |     | NULL    |       |
| name  | varchar(20)   | YES  |     | NULL    |       |
| sex   | enum('?','?') | YES  |     | NULL    |       |
+-------+---------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

中文乱码解决：

vim /etc/my.cnf
[client]
default-character-set=utf8 # [ˈkærəktər]

[mysqld]
character-set-server=utf8
collation-server=utf8_general_ci

mysql> alter table s1 add age int after name;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc s1;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| name  | varchar(50) | NO   |     | NULL    |                |
| age   | int(11)     | YES  |     | NULL    |                |
| sex   | varchar(10) | YES  |     | 男      |                |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

4.2.2 删除一列字段

alter table 表名 drop 字段名;

举例：

mysql> alter table s1 drop name;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

4.2.3 修改字段类型

alter table 表名 modify字段名新字段类型;

举例：
将sex字段类型有varchar 改为char

mysql> alter table s1 modify sex char;
Query OK, 3 rows affected (0.09 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> desc s1;
+-------+---------+------+-----+---------+----------------+
| Field | Type    | Null | Key | Default | Extra          |
+-------+---------+------+-----+---------+----------------+
| id    | int(11) | NO   | PRI | NULL    | auto_increment |
| age   | int(11) | YES  |     | NULL    |                |
| sex   | char(1) | YES  |     | NULL    |                |
+-------+---------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

4.2.4 修改字段名

alter table 表名 change 旧字段名新字段名字段类型;

举例：

mysql> alter table s1 change sex wg_sex varchar(20);
Query OK, 3 rows affected (0.09 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> desc s1;
+--------+-------------+------+-----+---------+----------------+
| Field  | Type        | Null | Key | Default | Extra          |
+--------+-------------+------+-----+---------+----------------+
| id     | int(11)     | NO   | PRI | NULL    | auto_increment |
| age    | int(11)     | YES  |     | NULL    |                |
| wg_sex | varchar(20) | YES  |     | NULL    |                |
+--------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

五：表的重命名

方法一：

alter table 表名 rename [to] 新表名；
举例：

mysql> alter table student rename to students;
Query OK, 0 rows affected (0.05 sec)

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| students       |
+----------------+
1 row in set (0.01 sec)

方法二：

rename table 旧表名 to 新表名;

mysql> rename table students to s1;
Query OK, 0 rows affected (0.01 sec)

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| s1             |
+----------------+
1 row in set (0.00 sec)

六：表的复制

6.1 只复制表结构

create table 新表名 like 旧表名;

举例：

mysql> create table s2 like s1;
Query OK, 0 rows affected (0.06 sec)

mysql> desc s2;
+--------+-------------+------+-----+---------+----------------+
| Field  | Type        | Null | Key | Default | Extra          |
+--------+-------------+------+-----+---------+----------------+
| id     | int(11)     | NO   | PRI | NULL    | auto_increment |
| age    | int(11)     | YES  |     | NULL    |                |
| wg_sex | varchar(20) | YES  |     | NULL    |                |
+--------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

mysql> select * from s2;
Empty set (0.00 sec)

6.2 表结构和数据一起复制

create table 新表名 select * from 旧表名;

举例：

mysql> create table s3 select  * from s1;
Query OK, 3 rows affected (0.07 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from s3;
+----+------+--------+
| id | age  | wg_sex |
+----+------+--------+
|  1 | NULL | 男     |
|  2 | NULL | 女     |
|  3 | NULL | 女     |
+----+------+--------+
3 rows in set (0.00 sec)

七：表数据的常规操作：

7.1 insert语句

7.1.1：部分列插入的方法

insert into 表名(字段名1,字段名2,…) values(字段值1,字段值2,…) ;

举例：

mysql> insert into s1 (name,sex) values ('呵呵','女');
Query OK, 1 row affected (0.00 sec)

mysql> select * from s1;
+----+--------+------+
| id | name   | sex  |
+----+--------+------+
|  1 | 华仔   | 男   |
|  2 | 呵呵   | 女   |
+----+--------+------+
2 rows in set (0.00 sec)

7.1.2：全部列插入的方法

insert into 表名 values(字段值1,字段值2,字段值3,…);

举例：

mysql> insert into s1 values (3,'哈哈','女');
Query OK, 1 row affected (0.01 sec)

mysql> select * from s1;
+----+--------+------+
| id | name   | sex  |
+----+--------+------+
|  1 | 华仔   | 男   |
|  2 | 呵呵   | 女   |
|  3 | 哈哈   | 女   |
+----+--------+------+
3 rows in set (0.00 sec)

7.1.3：将查询结果插入的方法

insert into 表名1 select 字段 from 表名2

举例：

mysql> select * from s2;
Empty set (0.00 sec)

mysql> insert into s2 select * from s1;
Query OK, 3 rows affected, 1 warning (0.07 sec)
Records: 3  Duplicates: 0  Warnings: 1

mysql> select * from s2;
+----+------+--------+
| id | age  | wg_sex |
+----+------+--------+
|  1 | NULL | 男     |
|  2 | NULL | 女     |
|  3 | NULL | 女     |
+----+------+--------+
3 rows in set (0.00 sec)

7.2 delete语句

7.2.1: 删除所有记录

delete from 表名;

举例：

mysql> delete from s1;
Query OK, 3 rows affected (0.04 sec)

mysql> select * from s1;
Empty set (0.00 sec)

7.2.2: 删除满足指定条件的记录

delete from 表名 where 条件;

举例：

mysql> select * from s2;
+----+------+--------+
| id | age  | wg_sex |
+----+------+--------+
|  1 | NULL | 男     |
|  2 | NULL | 女     |
|  3 | NULL | 女     |
|  4 |   18 | NULL   |
+----+------+--------+
4 rows in set (0.00 sec)

mysql> delete from s2 where wg_sex='女';
Query OK, 2 rows affected (0.05 sec)

mysql> select * from s2;
+----+------+--------+
| id | age  | wg_sex |
+----+------+--------+
|  1 | NULL | 男     |
|  4 |   18 | NULL   |
+----+------+--------+
2 rows in set (0.00 sec)

7.3 update语句

update 表名 set 字段名=‘新的值’ [where 条件];

举例：

mysql> select * from s2;
+----+------+--------+
| id | age  | wg_sex |
+----+------+--------+
|  1 | NULL | 男     |
|  4 |   18 | NULL   |
+----+------+--------+
2 rows in set (0.00 sec)

mysql> update s2 set age='28' where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from s2;
+----+------+--------+
| id | age  | wg_sex |
+----+------+--------+
|  1 |   28 | 男     |
|  4 |   18 | NULL   |
+----+------+--------+
2 rows in set (0.00 sec)

7.4 select语句

7.4.1: select语句的基本结构

select 查询字段 from 表名 where 条件;

其中 * 代表所有字段

举例：

mysql> select * from student;
+----+-----------+------+------+
| id | name      | sex  | age  |
+----+-----------+------+------+
|  1 | huazai    | 男   |   18 |
|  2 | huazai007 | 男   |   28 |
|  3 | 007       | 女   |   38 |
|  4 | hehe      | 女   |   48 |
+----+-----------+------+------+
4 rows in set (0.00 sec)

7.4.2: limit 限制显示结果

举例：
显示2条数据

mysql> select * from student limit 2;
+----+-----------+------+------+--------+
| id | name      | sex  | age  | market |
+----+-----------+------+------+--------+
|  1 | huazai    | 男   |   18 | 晋南   |
|  2 | huazai007 | 男   |   28 | 晋南   |
+----+-----------+------+------+--------+
2 rows in set (0.00 sec)

7.4.3: 操作符

操作符	描述	实例
=	等号，检测两个值是否相等，如果相等返回true	(A = B) 返回false。
<>,!=	不等于，检测两个值是否相等，如果不相等返回true	(A != B) 返回 true。
>	大于号，检测左边的值是否大于右边的值, 如果左边的值大于右边的值返回true	(A > B) 返回false。
<	小于号，检测左边的值是否小于右边的值, 如果左边的值小于右边的值返回true	(A < B) 返回 true。
>	大于等于号，检测左边的值是否大于或等于右边的值, 如果左边的值大于或等于右边的值返回true	(A >= B) 返回false。
<=	小于等于号，检测左边的值是否小于或等于右边的值, 如果左边的值小于或等于右边的值返回true	(A <= B) 返回 true。
like	模糊匹配	like ‘张%’
and	表示和	id=2 and name=‘张三’
or	表示或	id=2 or name=‘张三’
between	选取介于两个值之间的数据范围。BETWEEN 同 AND 一起搭配使用	WHERE 字段1 BETWEEN value1 AND value2
in	匹配到相同值所在的行显示出来	age in (18,28,38)
not in	取反	age not in (18,28)

举例：（=）

mysql> select * from student where name='huazai';
+----+--------+------+------+
| id | name   | sex  | age  |
+----+--------+------+------+
|  1 | huazai | 男   |   18 |
+----+--------+------+------+
1 row in set (0.00 sec)

举例：（<）

mysql> select * from student where id<3;
+----+-----------+------+------+
| id | name      | sex  | age  |
+----+-----------+------+------+
|  1 | huazai    | 男   |   18 |
|  2 | huazai007 | 男   |   28 |
+----+-----------+------+------+
2 rows in set (0.00 sec)

举例：（like模糊匹配）

mysql> select * from student where name like 'he%';
+----+------+------+------+
| id | name | sex  | age  |
+----+------+------+------+
|  4 | hehe | 女   |   48 |
+----+------+------+------+
1 row in set (0.00 sec)

举例：（and 多个条件都符合才会显示！）

mysql> select * from student where name like 'hua%' and age=18;
+----+--------+------+------+
| id | name   | sex  | age  |
+----+--------+------+------+
|  1 | huazai | 男   |   18 |
+----+--------+------+------+
1 row in set (0.00 sec)

举例：（or 或；只要符合其中一个条件就显示）

mysql> select * from student where name='hehe' or age=18;
+----+--------+------+------+
| id | name   | sex  | age  |
+----+--------+------+------+
|  1 | huazai | 男   |   18 |
|  4 | hehe   | 女   |   48 |
+----+--------+------+------+
2 rows in set (0.00 sec)

举例：（between and）

mysql> select * from student where age between 18 and 38;
+----+-----------+------+------+
| id | name      | sex  | age  |
+----+-----------+------+------+
|  1 | huazai    | 男   |   18 |
|  2 | huazai007 | 男   |   28 |
|  3 | 007       | 女   |   38 |
+----+-----------+------+------+
3 rows in set (0.00 sec)

举例：（in 匹配到相同值所在的行显示出来）

mysql> select * from student where age in (18,28);
+----+-----------+------+------+
| id | name      | sex  | age  |
+----+-----------+------+------+
|  1 | huazai    | 男   |   18 |
|  2 | huazai007 | 男   |   28 |
+----+-----------+------+------+
2 rows in set (0.00 sec)

7.4.4: group by 分组

GROUP BY 语句根据一个或多个列对结果集进行分组。

在分组的列上我们可以使用 COUNT, SUM, AVG,等函数。

7.4.4.1 常用函数

函数	描述
max()	最大值
min()	最小值
sum()	求和
avg()	平均数
count()	统计个数

表student 新增字段：market（市场部）

mysql> alter table student add market varchar(20);
Query OK, 0 rows affected (0.10 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc student;
+--------+-------------+------+-----+---------+----------------+
| Field  | Type        | Null | Key | Default | Extra          |
+--------+-------------+------+-----+---------+----------------+
| id     | int(11)     | NO   | PRI | NULL    | auto_increment |
| name   | varchar(50) | NO   |     | NULL    |                |
| sex    | varchar(10) | YES  |     | 男      |                |
| age    | int(11)     | YES  |     | NULL    |                |
| market | varchar(20) | YES  |     | NULL    |                |
+--------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

原始数据如下：

mysql> select * from student ;
+----+-----------+------+------+--------+
| id | name      | sex  | age  | market |
+----+-----------+------+------+--------+
|  1 | huazai    | 男   |   18 | 晋南   |
|  2 | huazai007 | 男   |   28 | 晋南   |
|  3 | 007       | 女   |   38 | 河北   |
|  4 | hehe      | 女   |   48 | 河南   |
|  5 | 张三      | 女   |   20 | 晋南   |
|  6 | 李四      | 男   |   20 | 河南   |
|  7 | 王五      | 男   |   21 | 河北   |
+----+-----------+------+------+--------+
7 rows in set (0.00 sec)

举例1：[group by+count()]
统计每个市场部的男生有多少个？

mysql> select market,count(*) as num from student where sex='男' group by market;
+--------+-----+
| market | num |
+--------+-----+
| 晋南   |   2 |
| 河北   |   1 |
| 河南   |   1 |
+--------+-----+
3 rows in set (0.00 sec)

举例2：[group by+max()]
显示每个市场部男学员的最大年龄

mysql> select market,max(age) as max,name from student where sex='男' group by market;
+--------+------+--------+
| market | max  |   
+--------+------+--------+
| 晋南   |   28 |  |
| 河北   |   21 |   |
| 河南   |   20 |  |
+--------+------+--------+
3 rows in set (0.00 sec)

举例3:[group by+min()]

显示每个市场部女学员的最小年龄

mysql> select market,min(age) as min,name from student where sex='女' group by market;
+--------+------+--------+
| market | min  |   |
+--------+------+--------+
| 晋南   |   20 |   |
| 河北   |   38 |     |
| 河南   |   48 |    |
+--------+------+--------+
3 rows in set (0.00 sec)

举例4：[group by+avg()]
显示每个市场部男学员的平均年龄。

mysql> select market,avg(age) as avg from student where sex='男' group by market;
+--------+---------+
| market | avg     |
+--------+---------+
| 晋南   | 23.0000 |
| 河北   | 21.0000 |
| 河南   | 20.0000 |
+--------+---------+
3 rows in set (0.00 sec)

扩展（子查询）
查询每个市场部年龄最大的学员名称

MariaDB [test]> select  t1.name,t2.max_age,t1.market from s2 as t1,(select market,max(age) as max_age from s2 group by market) as t2 where t1.age=t2.max_age and t1.market=t2.market order by max_age desc;
+-----------+---------+--------+
| name      | max_age | market |
+-----------+---------+--------+
| 老大      |     100 | 内蒙   |
| 老色皮    |      88 | 春峰   |
| 李狗蛋    |      38 | 黑北   |
| 乔治      |      38 | 苏皖   |
| 佩佩      |      30 | 晋南   |
| 橙子      |      18 | 鄂中   |
+-----------+---------+--------+
6 rows in set (0.00 sec)

7.4.4.2 having用法

关键字having，用来对分组的结果进行筛选

where 和having的区别：
where：是聚合前做筛选
having：是聚合后做筛选

举例：[group by+having]
显示学员平均年龄大于30岁的市场部名称。

mysql> select market,avg(age) as avg  from student  group by market having avg>30;
+--------+---------+
| market | avg     |
+--------+---------+
| 河南   | 34.0000 |
+--------+---------+
1 row in set (0.00 sec)

举例：[group by+having ]
显示男学员人数大于1的市场部名称。

mysql> select market,count(1) as num  from student where sex='男' group by market having num >1;
+--------+-----+
| market | num |
+--------+-----+
| 晋南   |   2 |
+--------+-----+
1 row in set (0.00 sec)

7.4.5: order by 排序

举例：
显示晋南市场部的学员名称，性别，年龄，并按照年龄排序（默认升序）

mysql> select name,sex,age   from student where market='晋南' order by age;
+-----------+------+------+
| name      | sex  | age  |
+-----------+------+------+
| huazai    | 男   |   18 |
| 张三      | 女   |   20 |
| huazai007 | 男   |   28 |
+-----------+------+------+
3 rows in set (0.00 sec)

举例：

显示晋南市场部的学员名称，性别，年龄，并按照年龄排序（desc降序）

mysql> select name,sex,age   from student where market='晋南' order by age desc;
+-----------+------+------+
| name      | sex  | age  |
+-----------+------+------+
| huazai007 | 男   |   28 |
| 张三      | 女   |   20 |
| huazai    | 男   |   18 |
+-----------+------+------+
3 rows in set (0.00 sec)

举例：

统计每个市场部的人数，并排序

mysql> select market,count(1) as num  from student group by market order by num;
+--------+-----+
| market | num |
+--------+-----+
| 河北   |   2 |
| 河南   |   2 |
| 晋南   |   3 |
+--------+-----+
3 rows in set (0.00 sec)