Mysql-完整性约束

知识预览

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

一 介绍

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

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

============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||+-------+---------+------+-----+---------+-------+1 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

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||+--------------+-------------+------+-----+---------+-------+3 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

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 |+----+------+------+1 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

•  快速理解foreign key

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，越浪费存储空间

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,让员工信息表部门部分存储为部门ID-------可以解释为ID为变量名,实际名称为部门名字.

如何关联，即foreign key(关键字)

#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，必须保证唯一(变量表必须是唯一的)
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,'技术发展事业部'),(2,'艾人力资源部'),(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',1),(7,'张火箭',3),(8,'林子弹',1),(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 |+----+-------+--------+

• 如何找出两张表之间的关系 (多对一 & 一对多 & 多对多)

暂时未建立相应的表,两个表之间有相应的归属关系.比如:一个表中有另一个表的字段.字段值必须是单个的,不能是是多个值
如果两个表没啥关系,也就没有所谓一对一或者多对一的关系了.

分析步骤：#1、先站在左表的角度去找  左表 员工  右表 部门是否左表的多条记录的某字段值可以对应右表的一条记录，如果是，则证明左表的一个字段foreign key 右表一个字段（通常是id）#2、再站在右表的角度去找是否右表的多条记录的某字段值可以对应左表的一条记录，如果是，则证明右表的一个字段foreign key 左表一个字段（通常是id）#3、总结：#多对一： 一 的关键信息必须是不能重复的如果只有步骤1成立，则是左表多对一右表 如果只有步骤2成立，则是右表多对一左表#多对多  老师和班级如果步骤1和2同时成立，则证明这两张表时一个双向的多对一，即多对多,需要定义一个这两张表的关系表来专门存放二者的关系#一对一:如果1和2都不成立，而是左表的一条记录唯一对应右表的一条记录，反之亦然。这种情况很简单，就是在左表foreign key右表的基础上，将左表的外键字段设置成unique即可

三 建立表之间的关系

#一对多或称为多对一三张表：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);

 

 

 

#多对多三张表：出版社，作者信息，书多对多：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1 egon:1 九阳神功  2 九阴真经  3 九阴白骨爪  4 独孤九剑  5 降龙十巴掌  6 葵花宝典2 alex:1 九阳神功  6 葵花宝典3 yuanhao:  4 独孤九剑  5 降龙十巴掌  6 葵花宝典4 wpq:  1 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);

 

 

#一对一两张表：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);

例一：一个用户只有一个博客用户表：id  nameegonalexwupeiqi博客表  fk+uniqueid url name_id xxxx1 yyyy3 zzz2例二：一个管理员唯一对应一个用户用户表：id user  password egonxxxx alexyyyy管理员表：fk+uniqueid user_id password  1  xxxxx  2  yyyyy其他例子

七 作业

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：