mysql-表完整性约束

阅读目录

• 一 介绍
• 二 not null与default
• 三 unique
• 四 primary key
• 五 auto_increment
• 六 foreign key
• 七 总结

 

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一 介绍

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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'age int unsigned NOT NULL default 20 必须为正值（无符号） 不允许为空 默认是203. 是否是key主键 primary key外键 foreign key索引 (index,unique...)

二 not null与default

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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
create table tb1(
nid int not null defalut 2,
num int not null)

==================not null====================mysql> create table t1(id int); #id字段默认可以插入空mysql> desc t1;+-------+---------+------+-----+---------+-------+| Field | Type| Null | Key | Default | Extra |+-------+---------+------+-----+---------+-------+| id| int(11) | YES  | | NULL||+-------+---------+------+-----+---------+-------+mysql> insert into t1 values(); #可以插入空mysql> create table t2(id int not null); #设置字段id不为空mysql> desc t2;+-------+---------+------+-----+---------+-------+| Field | Type| Null | Key | Default | Extra |+-------+---------+------+-----+---------+-------+| id| int(11) | NO| | NULL||+-------+---------+------+-----+---------+-------+mysql> insert into t2 values(); #不能插入空ERROR 1364 (HY000): Field 'id' doesn't have a default value==================default====================#设置id字段有默认值后，则无论id字段是null还是not null，都可以插入空，插入空默认填入default指定的默认值mysql> create table t3(id int default 1);mysql> alter table t3 modify id int not null default 1;==================综合练习====================mysql> create table student(-> name varchar(20) not null,-> age int(3) unsigned not null default 18,-> sex enum('male','female') default 'male',-> hobby set('play','study','read','music') default 'play,music'-> );mysql> desc student;+-------+------------------------------------+------+-----+------------+-------+| Field | Type| Null | Key | Default| Extra |+-------+------------------------------------+------+-----+------------+-------+| name  | varchar(20)| NO| | NULL||| age| int(3) unsigned| NO| | 18 ||| sex| enum('male','female')  | YES  | | male||| hobby | set('play','study','read','music') | YES  | | play,music ||+-------+------------------------------------+------+-----+------------+-------+mysql> insert into student(name) values('egon');mysql> select * from student;+------+-----+------+------------+| name | age | sex  | hobby  |+------+-----+------+------------+| egon |  18 | male | play,music |+------+-----+------+------------+

三 unique

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============设置唯一约束 UNIQUE===============方法一：create table department1(id int,name varchar(20) unique,comment varchar(100));方法二：create table department2(id int,name varchar(20),comment varchar(100),constraint uk_name unique(name));mysql> insert into department1 values(1,'IT','技术');Query OK, 1 row affected (0.00 sec)mysql> insert into department1 values(1,'IT','技术');ERROR 1062 (23000): Duplicate entry 'IT' for key 'name'

mysql> create table t1(id int not null unique);Query OK, 0 rows affected (0.02 sec)mysql> desc t1;+-------+---------+------+-----+---------+-------+| Field | Type| Null | Key | Default | Extra |+-------+---------+------+-----+---------+-------+| id| int(11) | NO| PRI | NULL||+-------+---------+------+-----+---------+-------+row in set (0.00 sec)

create table service(id int primary key auto_increment,name varchar(20),host varchar(15) not null,port int not null,unique(host,port) #联合唯一);mysql> insert into service values-> (1,'nginx','192.168.0.10',80),-> (2,'haproxy','192.168.0.20',80),-> (3,'mysql','192.168.0.30',3306)-> ;Query OK, 3 rows affected (0.01 sec)Records: 3  Duplicates: 0  Waings: 0mysql> insert into service(name,host,port) values('nginx','192.168.0.10',80);ERROR 1062 (23000): Duplicate entry '192.168.0.10-80' for key 'host'

四 primary key

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primary key字段的值不为空且唯一

一个表中可以：

单列做主键
多列做主键（复合主键）

但一个表内只能有一个主键primary key

============单列做主键===============#方法一：not null+uniquecreate table department1(id int not null unique, #主键name varchar(20) not null unique,comment varchar(100));mysql> desc department1;+---------+--------------+------+-----+---------+-------+| Field| Type | Null | Key | Default | Extra |+---------+--------------+------+-----+---------+-------+| id  | int(11)  | NO| PRI | NULL||| name| varchar(20)  | NO| UNI | NULL||| comment | varchar(100) | YES  | | NULL||+---------+--------------+------+-----+---------+-------+rows in set (0.01 sec)#方法二：在某一个字段后用primary keycreate table department2(id int primary key, #主键name varchar(20),comment varchar(100));mysql> desc department2;+---------+--------------+------+-----+---------+-------+| Field| Type | Null | Key | Default | Extra |+---------+--------------+------+-----+---------+-------+| id  | int(11)  | NO| PRI | NULL||| name| varchar(20)  | YES  | | NULL||| comment | varchar(100) | YES  | | NULL||+---------+--------------+------+-----+---------+-------+rows in set (0.00 sec)#方法三：在所有字段后单独定义primary keycreate table department3(id int,name varchar(20),comment varchar(100),constraint pk_name primary key(id); #创建主键并为其命名pk_namemysql> desc department3;+---------+--------------+------+-----+---------+-------+| Field| Type | Null | Key | Default | Extra |+---------+--------------+------+-----+---------+-------+| id  | int(11)  | NO| PRI | NULL||| name| varchar(20)  | YES  | | NULL||| comment | varchar(100) | YES  | | NULL||+---------+--------------+------+-----+---------+-------+rows in set (0.01 sec)

==================多列做主键================create table service(ip varchar(15),port char(5),service_name varchar(10) not null,primary key(ip,port));mysql> desc service;+--------------+-------------+------+-----+---------+-------+| Field| Type| Null | Key | Default | Extra |+--------------+-------------+------+-----+---------+-------+| ip| varchar(15) | NO| PRI | NULL||| port | char(5) | NO| PRI | NULL||| service_name | varchar(10) | NO| | NULL||+--------------+-------------+------+-----+---------+-------+rows in set (0.00 sec)mysql> insert into service values-> ('172.16.45.10','3306','mysqld'),-> ('172.16.45.11','3306','mariadb')-> ;Query OK, 2 rows affected (0.00 sec)Records: 2  Duplicates: 0  Waings: 0mysql> insert into service values ('172.16.45.10','3306','nginx');ERROR 1062 (23000): Duplicate entry '172.16.45.10-3306' for key 'PRIMARY'

五 auto_increment

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约束字段为自动增长，被约束的字段必须同时被key约束

#不指定id，则自动增长create table student(id int primary key auto_increment,name varchar(20),sex enum('male','female') default 'male');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||+-------+-----------------------+------+-----+---------+----------------+mysql> insert into student(name) values-> ('egon'),-> ('alex')-> ;mysql> select * from student;+----+------+------+| id | name | sex  |+----+------+------+|  1 | egon | male ||  2 | alex | male |+----+------+------+#也可以指定idmysql> insert into student values(4,'asb','female');Query OK, 1 row affected (0.00 sec)mysql> insert into student values(7,'wsb','female');Query OK, 1 row affected (0.00 sec)mysql> select * from student;+----+------+--------+| id | name | sex|+----+------+--------+|  1 | egon | male||  2 | alex | male||  4 | asb  | female ||  7 | wsb  | female |+----+------+--------+#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, 4 rows affected (0.00 sec)mysql> select * from student;Empty set (0.00 sec)mysql> insert into student(name) values('ysb');mysql> select * from student;+----+------+------+| id | name | sex  |+----+------+------+|  8 | ysb  | male |+----+------+------+#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 (0.01 sec)mysql> insert into student(name) values('egon');Query OK, 1 row affected (0.01 sec)mysql> select * from student;+----+------+------+| id | name | sex  |+----+------+------+|  1 | egon | male |+----+------+------+row in set (0.00 sec)

#在创建完表后，修改自增字段的起始值mysql> create table student(-> id int primary key auto_increment,-> name varchar(20),-> sex enum('male','female') default 'male'-> );mysql> alter table student auto_increment=3;mysql> show create table student;.......ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mysql> insert into student(name) values('egon');Query OK, 1 row affected (0.01 sec)mysql> select * from student;+----+------+------+| id | name | sex  |+----+------+------+|  3 | egon | male |+----+------+------+row in set (0.00 sec)mysql> show create table student;.......ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8#也可以创建表时指定auto_increment的初始值，注意初始值的设置为表选项，应该放到括号外create table student(id int primary key auto_increment,name varchar(20),sex enum('male','female') default 'male')auto_increment=3;#设置步长sqlserver：自增步长基于表级别create table t1（id int。。。）engine=innodb,auto_increment=2 步长=2 default charset=utf8mysql自增的步长：show session variables like 'auto_inc%';#基于会话级别set session auth_increment_increment=2 #修改会话级别的步长#基于全局级别的set global auth_increment_increment=2 #修改全局级别的步长（所有会话都生效）#！！！注意了注意了注意了！！！If the value of auto_increment_offset is greater than that of auto_increment_increment, the value of auto_increment_offset is ignored. 翻译：如果auto_increment_offset的值大于auto_increment_increment的值，则auto_increment_offset的值会被忽略 比如：设置auto_increment_offset=3，auto_increment_increment=2mysql> set global auto_increment_increment=5;Query OK, 0 rows affected (0.00 sec)mysql> set global auto_increment_offset=3;Query OK, 0 rows affected (0.00 sec)mysql> show variables like 'auto_incre%'; #需要退出重新登录+--------------------------+-------+| Variable_name| Value |+--------------------------+-------+| auto_increment_increment | 1 || auto_increment_offset| 1 |+--------------------------+-------+create table student(id int primary key auto_increment,name varchar(20),sex enum('male','female') default 'male');mysql> insert into student(name) values('egon1'),('egon2'),('egon3');mysql> select * from student;+----+-------+------+| id | name  | sex  |+----+-------+------+|  3 | egon1 | male ||  8 | egon2 | male || 13 | egon3 | male |+----+-------+------+

六 foreign key

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员工信息表有三个字段：工号  姓名  部门

公司有3个部门，但是有1个亿的员工，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

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

#表类型必须是innodb存储引擎，且被关联的字段，即references指定的另外一个表的字段，必须是主键create table department(id int primary key,name varchar(20) not null)engine=innodb;#dpt_id外键，关联父表（department主键id），同步更新，同步删除create table employee(id int primary key,name varchar(20) not null,dpt_id int,constraint fk_name foreign key(dpt_id)references department(id)on delete cascadeon update cascade )engine=innodb;#先往父表department中插入记录insert into department values(1,'欧德博爱技术有限事业部'),(2,'艾利克斯人力资源部'),(3,'销售部');#再往子表employee中插入记录insert into employee values(1,'egon',1),(2,'alex1',2),(3,'alex2',2),(4,'alex3',2),(5,'李坦克',3),(6,'刘飞机',3),(7,'张火箭',3),(8,'林子弹',3),(9,'加特林',3);#删父表department，子表employee中对应的记录跟着删mysql> delete from department where id=3;mysql> select * from employee;+----+-------+--------+| id | name  | dpt_id |+----+-------+--------+|  1 | egon  |  1 ||  2 | alex1 |  2 ||  3 | alex2 |  2 ||  4 | alex3 |  2 |+----+-------+--------+#更新父表department，子表employee中对应的记录跟着改mysql> update department set id=22222 where id=2;mysql> select * from employee;+----+-------+--------+| id | name  | dpt_id |+----+-------+--------+|  1 | egon  |  1 ||  3 | alex2 |  22222 ||  4 | alex3 |  22222 ||  5 | alex1 |  22222 |+----+-------+--------+

表1 foreign key 表2则表1的多条记录对应表2的一条记录，即多对一利用foreign key的原理我们可以制作两张表的多对多，一对一关系多对多：表1的多条记录可以对应表2的一条记录表2的多条记录也可以对应表1的一条记录一对一：表1的一条记录唯一对应表2的一条记录，反之亦然分析时，我们先从按照上面的基本原理去套，然后再翻译成真实的意义，就很好理解了、、

三张表：出版社，作者信息，书

一对多（或多对一）：一个出版社可以出版多本书

　　关联方式：foreign key

=====================多对一=====================create table press(id int primary key auto_increment,name varchar(20));create table book(id int primary key auto_increment,name varchar(20),press_id int not null,foreign key(press_id) references press(id)on delete cascadeon update cascade);insert into press(name) values('北京工业地雷出版社'),('人民音乐不好听出版社'),('知识产权没有用出版社');insert into book(name,press_id) values('九阳神功',1),('九阴真经',2),('九阴白骨爪',2),('独孤九剑',3),('降龙十巴掌',2),('葵花宝典',3);

多对多：一个作者可以写多本书，一本书也可以有多个作者，双向的一对多，即多对多

　　关联方式：foreign key+一张新的表

=====================多对多=====================create table author(id int primary key auto_increment,name varchar(20));#这张表就存放作者表与书表的关系，即查询二者的关系查这表就可以了create table author2book(id int not null unique auto_increment,author_id int not null,book_id int not null,constraint fk_author foreign key(author_id) references author(id)on delete cascadeon update cascade,constraint fk_book foreign key(book_id) references book(id)on delete cascadeon update cascade,primary key(author_id,book_id));#插入四个作者，id依次排开insert into author(name) values('egon'),('alex'),('yuanhao'),('wpq');#每个作者与自己的代表作如下egon: 九阳神功九阴真经九阴白骨爪独孤九剑降龙十巴掌葵花宝典alex: 九阳神功葵花宝典yuanhao:独孤九剑降龙十巴掌葵花宝典wpq:九阳神功insert into author2book(author_id,book_id) values(1,1),(1,2),(1,3),(1,4),(1,5),(1,6),(2,1),(2,6),(3,4),(3,5),(3,6),(4,1);

#两张表：学生表和客户表

一对一：一个学生是一个客户，一个客户有可能变成一个学校，即一对一的关系

　　关联方式：foreign key+unique

#一定是student来foreign key表customer，这样就保证了：#1 学生一定是一个客户，#2 客户不一定是学生，但有可能成为一个学生create table customer(id int primary key auto_increment,name varchar(20) not null);create table student(id int primary key auto_increment,name varchar(20) not null,class_name varchar(20) not null default 'python自动化',level int default 1,customer_id int unique, #该字段一定要是唯一的foreign key(customer_id) references customer(id) #外键的字段一定要保证uniqueon delete cascadeon update cascade);#增加客户insert into customer(name) values('李飞机'),('王大炮'),('守榴弹'),('吴坦克'),('赢火箭'),('战地雷');#增加学生insert into student(name,customer_id) values('李飞机',1),('王大炮',2);

练习：账号信息表，用户组，主机表，主机组

#用户表create table user(id int not null unique auto_increment,useame varchar(20) not null,password varchar(50) not null,primary key(useame,password));insert into user(useame,password) values('root','123'),('egon','456'),('alex','alex3714');#用户组表create table usergroup(id int primary key auto_increment,groupname varchar(20) not null unique);insert into usergroup(groupname) values('IT'),('Sale'),('Finance'),('boss');#主机表create table host(id int primary key auto_increment,ip char(15) not null unique default '127.0.0.1');insert into host(ip) values('172.16.45.2'),('172.16.31.10'),('172.16.45.3'),('172.16.31.11'),('172.10.45.3'),('172.10.45.4'),('172.10.45.5'),('192.168.1.20'),('192.168.1.21'),('192.168.1.22'),('192.168.2.23'),('192.168.2.223'),('192.168.2.24'),('192.168.3.22'),('192.168.3.23'),('192.168.3.24');#业务线表create table business(id int primary key auto_increment,business varchar(20) not null unique);insert into business(business) values('轻松贷'),('随便花'),('大富翁'),('穷一生');#建关系：user与usergroupcreate table user2usergroup(id int not null unique auto_increment,user_id int not null,group_id int not null,primary key(user_id,group_id),foreign key(user_id) references user(id),foreign key(group_id) references usergroup(id));insert into user2usergroup(user_id,group_id) values(1,1),(1,2),(1,3),(1,4),(2,3),(2,4),(3,4);#建关系：host与businesscreate table host2business(id int not null unique auto_increment,host_id int not null,business_id int not null,primary key(host_id,business_id),foreign key(host_id) references host(id),foreign key(business_id) references business(id));insert into host2business(host_id,business_id) values(1,1),(1,2),(1,3),(2,2),(2,3),(3,4);#建关系：user与hostcreate table user2host(id int not null unique auto_increment,user_id int not null,host_id int not null,primary key(user_id,host_id),foreign key(user_id) references user(id),foreign key(host_id) references host(id));insert into user2host(user_id,host_id) values(1,1),(1,2),(1,3),(1,4),(1,5),(1,6),(1,7),(1,8),(1,9),(1,10),(1,11),(1,12),(1,13),(1,14),(1,15),(1,16),(2,2),(2,3),(2,4),(2,5),(3,10),(3,11),(3,12);

 

作业：

七、总结

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1 not null 与defaultcreate table student2(id int primary key auto_increment,name char(5),sex enum('male','female') not null default 'female');insert into student2(name) values('alex');create table student3(id int primary key auto_increment,name char(5),age int not null default 30);insert into student3(name) values('alex');2 unique#单列唯一create table teacher(id int not null unique,name char(10));insert into teacher values(1,'egon');insert into teacher values(1,'alex');#多列唯一#255.255.255.255create table services(id int primary key auto_increment,name char(10),host char(15),port int,constraint host_port unique(host,port));insert into services values('ftp','192.168.20.17',8080);insert into services values('httpd','192.168.20.17',8081);#auto_increment_offset:偏移量create table dep(id int primary key auto_increment,name char(10));insert into dep(name) values('IT'),('HR'),('SALE'),('Boss');create table dep1(id int primary key auto_increment,name char(10))auto_increment=10;insert into dep1(name) values('IT'),('HR'),('SALE'),('Boss');#auto_increment_increment:步长create table dep2(id int primary key auto_increment,name char(10));set session auto_increment_increment=2; #会话级，只对当前会话有效set global auto_increment_increment=2; #全局，对所有的会话都有效insert into dep1(name) values('IT'),('HR'),('SALE'),('Boss');#auto_increment_offset:偏移量+auto_increment_increment:步长注意：如果auto_increment_offset的值大于auto_increment_increment的值，则auto_increment_offset的值会被忽略set session auto_increment_offset=2;set session auto_increment_increment=3;show variables like '%auto_in%';create table dep3(id int primary key auto_increment,name char(10));insert into dep3(name) values('IT'),('HR'),('SALE'),('Boss');#foreign key#！！！先建被关联的表,并且被关联的字段必须唯一create table dep(id int primary key auto_increment,name varchar(50),comment varchar(100));create table emp_info(id int primary key auto_increment,name varchar(20),dep_id int,constraint fk_depid_id foreign key(dep_id) references dep(id)on delete cascadeon update cascade);#先给被关联的表初始化记录insert into dep values(1,'欧德博爱技术有限事业部','说的好...'),(2,'艾利克斯人力资源部','招不到人'),(3,'销售部','卖不出东西');insert into emp_info values(1,'egon',1),(2,'alex1',2),(3,'alex2',2),(4,'alex3',2),(5,'李坦克',3),(6,'刘飞机',3),(7,'张火箭',3),(8,'林子弹',3),(9,'加特林',3);