mysql-完整性约束

约束条件与数据类型的宽度一样，都是可选参数

作用：用于保证数据的完整性和一致性

主要分为：

PRIMARY KEY (PK)    #标识该字段为该表的主键，可以唯一的标识记录
FOREIGN KEY (FK)    #标识该字段为该表的外键
NOT NULL            #标识该字段不能为空
UNIQUE KEY (UK)     #标识该字段的值是唯一的
AUTO_INCREMENT      #标识该字段的值自动增长（整数类型，而且为主键）
DEFAULT             #为该字段设置默认值

UNSIGNED            #无符号
ZEROFILL            #使用0填充

说明:

#1. 是否允许为空，默认NULL，可设置NOT NULL，字段不允许为空，必须赋值
#2. 字段是否有默认值，缺省的默认值是NULL，如果插入记录时不给字段赋值，此字段使用默认值
sex enum('male','female') not null default 'male'

#必须为正值（无符号） 不允许为空 默认是20
age int unsigned NOT NULL default 20 
# 3. 是否是key
主键 primary key
外键 foreign key
索引 (index,unique...)

not null 与default

是否可空，null表示空，非字符串

not null - 不可空

null - 可空

默认值，创建列时可以指定默认值，当插入数据时如果未主动设置，则自动添加默认值

mysql> create database db1;  # 创建db1数据库

Query OK, 1 row affected (0.00 sec)

mysql> use db1;  # 选择db1数据库

Database changed

mysql> create table tb1(id int not null default 2,num int not null);  # 创建tb1表并约束

Query OK, 0 rows affected (0.03 sec)

mysql> desc tb1;  # 查看tb1表结构

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

| Field | Type    | Null | Key | Default | Extra |

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

| id    | int(11) | NO   |     | 2       |       |

| num   | int(11) | NO   |     | NULL    |       |

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

2 rows in set (0.00 sec)

验证1：

mysql> create table t11(id int);  # 创建t11表 id字段默认可以为空

Query OK, 0 rows affected (0.16 sec)

mysql> desc t11;  # 查看t11表结构

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

| Field | Type    | Null | Key | Default | Extra |

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

| id    | int(11) | YES  |     | NULL    |       |

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

1 row in set (0.00 sec)

mysql> select * from  t11;  # 查看t11表数据为空

Empty set (0.00 sec)

mysql> insert into t11 values();  # 在t11表中插入一个空值

Query OK, 1 row affected (0.00 sec)

mysql> select * from  t11;  # 查看t11表数据，可以看到一个NULL的值

+------+

| id   |

+------+

| NULL |

+------+

1 row in set (0.00 sec)

验证2：

mysql> create table t12(id int not null);

Query OK, 0 rows affected (0.05 sec)

mysql> desc t12;

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

| Field | Type    | Null | Key | Default | Extra |

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

| id    | int(11) | NO   |     | NULL    |       |

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

1 row in set (0.00 sec)

mysql> insert into t12 values();

ERROR 1364 (HY000): Field 'id' doesn't have a default value

验证3:

第一种情况

mysql> create table t13(id int default 1);

Query OK, 0 rows affected (0.11 sec)

mysql> desc t13;

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

| Field | Type    | Null | Key | Default | Extra |

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

| id    | int(11) | YES  |     | 1       |       |

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

1 row in set (0.00 sec)

mysql> insert into t13 values();

Query OK, 1 row affected (0.01 sec)

mysql> select * from t13;

+------+

| id   |

+------+

|    1 |

+------+

1 row in set (0.00 sec)

第二种情况:

mysql> create table t14(id int not null default 2);

Query OK, 0 rows affected (0.40 sec)

mysql> desc t14;

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

| Field | Type    | Null | Key | Default | Extra |

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

| id    | int(11) | NO   |     | 2       |       |

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

1 row in set (0.01 sec)

mysql> select * from t14;

Empty set (0.00 sec)

mysql> insert into t14 values();

Query OK, 1 row affected (0.01 sec)

mysql> select * from t14;

+----+

| id |

+----+

|  2 |

+----+

1 row in set (0.00 sec)

练习:

创建学生表student2,设置每个字段的约束条件.

mysql> create table student2(id int not null,name varchar(50) not null,age int(3) unsigned  not null default 18,sex enum('male','female') default 'male', fav set('smoke','drink','tanngtou') default 'drink,tangtou');

Query OK, 0 rows affected (0.38 sec)

# 只插入了not null约束条件的字段对应的值

mysql> insert into student2(id,name) values(1,'张三');

Query OK, 1 row affected (0.00 sec)

mysql> select * from student2;

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

| id | name   | age | sex  | fav           |

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

|  1 | 张三   |  18 | male | drink,tangtou |

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

1 row in set (0.00 sec)

unique,在mysql中称为单列唯一

举例说明：创建公司部门表（每个公司都有唯一的一个部门）

mysql> create table department(id int,name char(10));

Query OK, 0 rows affected (0.03 sec)

mysql> insert into department values(1,'IT'),(2,'IT');

Query OK, 2 rows affected (0.01 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from department;

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

| id   | name |

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

|    1 | IT   |

|    2 | IT   |

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

2 rows in set (0.00 sec)

发现:同时插入两个IT部门也是可以的，但这是不合理的，所以我们要设置name字段为unique解决这种不合理的现象。

接下来，使用约束条件unique，来对公司部门的字段进行设置

第一种创建unique的方式

例子1

mysql> create table department1(id int,name char(10) unique);

Query OK, 0 rows affected (0.10 sec)

mysql> insert into departement1 values(1,'张三'),(2,'张三');  # name的值不唯一，报错

ERROR 1146 (42S02): Table 'db1.departement1' doesn't exist

例子2

mysql> create table department2(id int unique,name char(10) unique);

Query OK, 0 rows affected (0.11 sec)

mysql> insert into department2 values(1,'张三'),(2,'李四');

Query OK, 2 rows affected (0.38 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from department2;

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

| id   | name   |

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

|    1 | 张三   |

|    2 | 李四   |

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

2 rows in set (0.00 sec)

第二种创建unique的方式

mysql> create table department3(id int,name char(10), unique(id),unique(name));

Query OK, 0 rows affected (0.12 sec)

mysql> insert into department3 values(1,'哈哈'),(2,'嘿嘿');

Query OK, 2 rows affected (0.01 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from department3;

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

| id   | name   |

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

|    1 | 哈哈   |

|    2 | 嘿嘿   |

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

2 rows in set (0.00 sec)

联合唯一:

创建services表

mysql> create table services(id int,ip char(15),port int,unique(id),unique(ip,port));

Query OK, 0 rows affected (0.44 sec)

mysql> desc services;

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

| Field | Type     | Null | Key | Default | Extra |

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

| id    | int(11)  | YES  | UNI | NULL    |       |

| ip    | char(15) | YES  | MUL | NULL    |       |

| port  | int(11)  | YES  |     | NULL    |       |

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

3 rows in set (0.00 sec)

# 联合唯一，只要两列记录，有一列不同，既符合联合唯一的约束

mysql> insert into services values(1,'192.168.11.23',80),(2,'192.168.11.23',81),(3,'192.168.11.25',80);

Query OK, 3 rows affected (0.01 sec)

Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from services;

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

| id   | ip            | port |

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

|    1 | 192.168.11.23 |   80 |

|    2 | 192.168.11.23 |   81 |

|    3 | 192.168.11.25 |   80 |

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

3 rows in set (0.00 sec)

mysql> insert into services values(4,'192.168.11.23',80);  # 报错,不满足联合唯一原则

ERROR 1062 (23000): Duplicate entry '192.168.11.23-80' for key 'ip'

primary key

一个表中可以：

单列做主键

多列做主键（复合主键）

约束：等价于 not null unique,字段的值不为空且唯一

存储引擎默认是（innodb）:对于innodb存储引擎来说，一张表必须有一个主键

单列主键

# 创建t14表，为id字段设置主键，唯一的不同的记录

mysql> create table t14(id int primary key,name char(16));

Query OK, 0 rows affected (0.04 sec)

mysql> insert into t14 values(1,'小黑'),(2,'小白');

Query OK, 2 rows affected (0.00 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> insert into t14 values(2,'wxxx');  #设置id为主键，主键内容不能重复

ERROR 1062 (23000): Duplicate entry '2' for key 'PRIMARY'

# not null + unique的化学反应，相当于给id设置primary key

mysql> create table t15(id int not null unique,name char(16));

Query OK, 0 rows affected (0.39 sec)

mysql> desc t15;

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

| Field | Type     | Null | Key | Default | Extra |

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

| id    | int(11)  | NO   | PRI | NULL    |       |

| name  | char(16) | YES  |     | NULL    |       |

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

2 rows in set (0.00 sec)

mysql> insert into t15 values(1,'小黑'),(2,'小白');

Query OK, 2 rows affected (0.01 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> insert into t15 values(2,'小花');  # 报错，主键不能相同

ERROR 1062 (23000): Duplicate entry '2' for key 'id'

符合主键

mysql> create table t16(ip char(15), port int, primary key(ip,port));

Query OK, 0 rows affected (0.09 sec)

mysql> insert into t16 values('192.168.11.22',80),('192.168.11.22',81);

Query OK, 2 rows affected (0.00 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from t16;

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

| ip            | port |

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

| 192.168.11.22 |   80 |

| 192.168.11.22 |   81 |

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

2 rows in set (0.00 sec)

auto_increment

约束:约束的字段为自动增长，约束的字段必须同时被key约束

(重点)验证:

不指定id，则自动增长

mysql> create table student(id int primary key auto_increment,name varchar(20),sex enum('maale','female') default 'male');

Query OK, 0 rows affected (0.04 sec)

mysql> desc student;

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

| Field | Type                  | Null | Key | Default | Extra          |

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

| id    | int(11)               | NO   | PRI | NULL    | auto_increment |

| name  | varchar(20)           | YES  |     | NULL    |                |

| sex   | enum('male','female') | YES  |     | male    |                |

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

3 rows in set (0.00 sec)

# 插入记录

mysql> insert into student(name) values('哈哈'),('嘿嘿');

Query OK, 2 rows affected (0.00 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from student;

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

| id | name   | sex  |

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

|  1 | 哈哈   | male |

|  2 | 嘿嘿   | male |

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

2 rows in set (0.00 sec)

也可以指定id

mysql> insert into student values(4,'asb','female');

Query OK, 1 row affected (0.01 sec)

mysql> insert into student values(7,'web','female');

Query OK, 1 row affected (0.00 sec)

mysql> select * from student;

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

| id | name   | sex    |

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

|  1 | 哈哈   | male   |

|  2 | 嘿嘿   | male   |

|  4 | asb    | female |

|  7 | web    | female |

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

4 rows in set (0.00 sec)

# 再次插入一条不指定id的记录，会在之前的最后一条记录继续增长

mysql> insert into student(name) values('哦哦');

Query OK, 1 row affected (0.01 sec)

mysql> select * from student;

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

| id | name   | sex    |

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

|  1 | 哈哈   | male   |

|  2 | 嘿嘿   | male   |

|  4 | asb    | female |

|  7 | web    | female |

|  8 | 哦哦   | male   |

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

5 rows in set (0.00 sec)

对于自增的字段，在用delete删除后，再插入值，该字段仍按照删除前的位置继续增长

mysql> delete from student;

Query OK, 5 rows affected (0.00 sec)

mysql> select * from student;

Empty set (0.00 sec)

mysql> insert into student(name) values('嗯嗯');

Query OK, 1 row affected (0.00 sec)

mysql> select * from student;

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

| id | name   | sex  |

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

|  9 | 嗯嗯   | male |

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

1 row in set (0.00 sec)

# 应该用truncate清空表，比起delete一条一条地删除记录，truncate是直接清空表，在删除大表时用它

mysql> truncate student;

Query OK, 0 rows affected (0.02 sec)

mysql> insert into student(name) values('呃呃');

Query OK, 1 row affected (0.01 sec)

mysql> select * from student;

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

| id | name   | sex  |

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

|  1 | 呃呃   | male |

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

1 row in set (0.00 sec)

清空表区分delete和truncate的区别：

delete from t1; 如果有自增id，新增的数据，仍然是以删除前的最后一样作为起始.

truncate table t1;数据量大，删除速度比上一条快，且直接从零开始.

foreign key

公司有3个部门，但是很多的员工，那意味着部门这个字段需要重复存储，部门名字越长，越浪费。

这个时候，

解决方法：

我们完全可以定义一个部门表

然后让员工信息表关联该表，如何关联，即foreign key

我们可以将上表改为如下结构：

此时有两张表，一张是employee表,简称emp表（关联表，也就主表）。一张是department表，简称dep表（被关联表，也叫从表）

创建两张表操作:

1 创建表时先创建主表，再创建关联表 

先创建主表(dep表)

mysql> create table dep(id int primary key,name varchar(20) not null,descripe varchar(20) not null);

Query OK, 0 rows affected (0.42 sec)

再创建关联表(emp表)

mysql> create table emp(

         id int primary key,

         name varchar(20) not null,

         age int not null,

         dep_id int,

         constraint fk_dep foreign key(dep_id) references dep(id) 

     );

Query OK, 0 rows affected (0.11 sec)

2 插入记录时，先往被关联表中插入记录，再往关联表中插入记录

mysql> insert into dep values

     (1,'IT','IT技术有限部门'),

     (2,'销售部','销售部门'),

     (3,'财务部','花钱太多部门');

Query OK, 3 rows affected (0.00 sec)

Records: 3  Duplicates: 0  Warnings: 0

mysql> insert into emp values

     (1,'zhangsan',18,1),

     (2,'lisi',19,1),

     (3,'wangwu',20,2),

     (4,'zhuliu',40,3),

     (5,'chenqi',18,2);

Query OK, 5 rows affected (0.01 sec)

Records: 5  Duplicates: 0  Warnings: 0

3 删除表

按道理来说，删除了部门表中的某个部门，员工表的有关联的记录相继删除

mysql> delete from dep where id=3; # 报错，应该先删除被关联表

ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`db1`.`emp`, CONSTRAINT `fk_dep` FOREIGN KEY (`dep_id`) REFERENCES `dep` (`id`))

但是先删除员工表的记录之后，再删除当前部门就没有任何问题

mysql> delete from emp where id=3;

Query OK, 1 row affected (0.01 sec)

mysql> delete from emp where id=4;

Query OK, 1 row affected (0.01 sec)

mysql> select * from emp;

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

| id | name     | age | dep_id |

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

|  1 | zhangsan |  18 |      1 |

|  2 | lisi     |  19 |      1 |

|  5 | chenqi   |  18 |      2 |

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

3 rows in set (0.01 sec)

4 rows in set (0.00 sec)

mysql> delete from dep where id=3;

Query OK, 1 row affected (0.00 sec)

mysql> select * from dep;

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

| id | name      | descripe             |

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

|  1 | IT        | IT技术有限部门       |

|  2 | 销售部    | 销售部门             |

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

2 rows in set (0.00 sec)

上面的删除表记录的操作比较繁琐，按道理讲，裁掉一个部门，该部门的员工也会被裁掉。其实呢，在建表的时候还有个很重要的内容，叫同步删除，同步更新

接下来将刚建好的两张表全部删除，先删除关联表（emp）,再删除被关联表（dep）

接下来：

重复上面的操作建表

注意：在关联表中加入

on delete cascade #同步删除

on update cascade #同步更新

删除表

mysql> drop table emp;

Query OK, 0 rows affected (0.12 sec)

mysql> drop table dep;

Query OK, 0 rows affected (0.01 sec)

创建表

mysql> create table dep(

         id int primary key,

         name varchar(20) not null,

         descripe varchar(20) not null

     );

Query OK, 0 rows affected (0.04 sec)

mysql> create table emp(

         id int primary key,

         name varchar(20) not null,

         age int not null,

         dep_id int,

         constraint fk_dep foreign key(dep_id) references dep(id) 

         on delete cascade  # 同步删除

         on update cascade  # 同步更新

     );

Query OK, 0 rows affected (0.06 sec)

插入数据:

mysql> insert into dep values

     (1,'IT','IT技术有限部门'),

     (2,'销售部','销售部门'),

     (3,'财务部','花钱太多部门');

Query OK, 3 rows affected (0.01 sec)

Records: 3  Duplicates: 0  Warnings: 0

mysql> insert into emp values

     (1,'zhangsan',18,1),

     (2,'lisi',19,1),

     (3,'wangwu',20,2),

     (4,'zhuliu',40,3),

     (5,'chenqi',18,2);

Query OK, 5 rows affected (0.01 sec)

Records: 5  Duplicates: 0  Warnings: 0

接下来的操作，就复合我们正常的生活中的情况了

再去删被关联表(dep)的记录，关联表(emp)中的记录也跟着删除

mysql> delete from dep where id=3;

Query OK, 1 row affected (0.00 sec)

mysql> select * from dep;

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

| id | name      | descripe             |

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

|  1 | IT        | IT技术有限部门       |

|  2 | 销售部    | 销售部门             |

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

2 rows in set (0.00 sec)

mysql> select * from emp;

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

| id | name     | age | dep_id |

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

|  1 | zhangsan |  18 |      1 |

|  2 | lisi     |  19 |      1 |

|  3 | wangwu   |  20 |      2 |

|  5 | chenqi   |  18 |      2 |

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

4 rows in set (0.00 sec)

再去更改被关联表(dep)的记录，关联表(emp)中的记录也跟着更改

mysql> update dep set id=222 where id=2;

Query OK, 1 row affected (0.03 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from dep;

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

| id  | name      | descripe             |

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

|   1 | IT        | IT技术有限部门       |

| 222 | 销售部    | 销售部门             |

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

2 rows in set (0.00 sec)

mysql> select * from emp;

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

| id | name     | age | dep_id |

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

|  1 | zhangsan |  18 |      1 |

|  2 | lisi     |  19 |      1 |

|  3 | wangwu   |  20 |    222 |

|  5 | chenqi   |  18 |    222 |

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

4 rows in set (0.00 sec)