mysql-完整性约束

发布时间:2018-06-13 17:05:23编辑:Run阅读(3791)

    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:

    blob.png

    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)




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