表的完整性约束
阅读目录
目录:
not noll
unique
primary key
foreign key
概览
为了防止不符合规范的数据进入数据库,在用户对数据进行插入、修改、删除等操作时,DBMS自动按照一定的约束条件对数据进行监测,使不符合规范的数据不能进入数据库,以确保数据库中存储的数据正确、有效、相容。
约束条件与数据类型的宽度一样,都是可选参数,主要分为以下几种:
# NOT NULL :非空约束,指定某列不能为空; # UNIQUE : 唯一约束,指定某列或者几列组合不能重复 # PRIMARY KEY :主键,指定该列的值可以唯一地标识该列记录 # FOREIGN KEY :外键,指定该行记录从属于主表中的一条记录,主要用于参照完整性
NOT NULL
是否可空,null表示空,非字符串
not null - 不可空
null - 可空

mysql> create table t12 (id int not null); Query OK, 0 rows affected (0.02 sec) mysql> select * from t12; Empty set (0.00 sec) mysql> desc t12; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | NO | | NULL | | +-------+---------+------+-----+---------+-------+ row in set (0.00 sec) #不能向id列插入空元素。 mysql> insert into t12 values (null); ERROR 1048 (23000): Column 'id' cannot be null mysql> insert into t12 values (1); Query OK, 1 row affected (0.01 sec)
DEFAULT
我们约束某一列不为空,如果这一列中经常有重复的内容,就需要我们频繁的插入,这样会给我们的操作带来新的负担,于是就出现了默认值的概念。
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 table t13 (id1 int not null,id2 int not null default 222); Query OK, 0 rows affected (0.01 sec) mysql> desc t13; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id1 | int(11) | NO | | NULL | | | id2 | int(11) | NO | | 222 | | +-------+---------+------+-----+---------+-------+ rows in set (0.01 sec) # 只向id1字段添加值,会发现id2字段会使用默认值填充 mysql> insert into t13 (id1) values (111); Query OK, 1 row affected (0.00 sec) mysql> select * from t13; +-----+-----+ | id1 | id2 | +-----+-----+ | 111 | 222 | +-----+-----+ row in set (0.00 sec) # id1字段不能为空,所以不能单独向id2字段填充值; mysql> insert into t13 (id2) values (223); ERROR 1364 (HY000): Field 'id1' doesn't have a default value # 向id1,id2中分别填充数据,id2的填充数据会覆盖默认值 mysql> insert into t13 (id1,id2) values (112,223); Query OK, 1 row affected (0.00 sec) mysql> select * from t13; +-----+-----+ | id1 | id2 | +-----+-----+ | 111 | 222 | | 112 | 223 | +-----+-----+ rows in set (0.00 sec)

设置严格模式: 不支持对not null字段插入null值 不支持对自增长字段插入”值 不支持text字段有默认值 直接在mysql中生效(重启失效): mysql>set sql_mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"; 配置文件添加(永久失效): sql-mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"
UNIQUE
唯一约束,指定某列或者几列组合不能重复

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), 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 Warnings: 0 mysql> 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'
PRIMARY KEY
主键为了保证表中的每一条数据的该字段都是表格中的唯一值。换言之,它是用来独一无二地确认一个表格中的每一行数据。
主键可以包含一个字段或多个字段。当主键包含多个栏位时,称为组合键 (Composite Key),也可以叫联合主键。
主键可以在建置新表格时设定 (运用 CREATE TABLE 语句),或是以改变现有的表格架构方式设定 (运用 ALTER TABLE)。
主键必须唯一,主键值非空;可以是单一字段,也可以是多字段组合。
1.单字段主键

============单列做主键=============== #方法一:not null+unique create 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 key create 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 key create table department3( id int, name varchar(20), comment varchar(100), primary key(id); #创建主键并为其命名pk_name mysql> 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) # 方法四:给已经建成的表添加主键约束 mysql> create table department4( -> id int, -> name varchar(20), -> comment varchar(100)); Query OK, 0 rows affected (0.01 sec) mysql> desc department4; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | varchar(20) | YES | | NULL | | | comment | varchar(100) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ rows in set (0.01 sec) mysql> alter table department4 modify id int primary key; Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc department4; +---------+--------------+------+-----+---------+-------+ | 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)
2.多字段主键

==================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 Warnings: 0 mysql> insert into service values ('172.16.45.10','3306','nginx'); ERROR 1062 (23000): Duplicate entry '172.16.45.10-3306' for key 'PRIMARY'
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id mysql> 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)
了解知识

#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=utf8 mysql> 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=utf8 mysql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 ,这相当于第一步步子就迈大了,扯着了蛋 比如:设置auto_increment_offset=3,auto_increment_increment=2 mysql> 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 | +----+-------+------+ 步长:auto_increment_increment,起始偏移量:auto_increment_offset
FOREIKEY
多表 :
假设我们要描述所有公司的员工,需要描述的属性有这些 : 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

mysql> create table departments (dep_id int(4),dep_name varchar(11)); Query OK, 0 rows affected (0.02 sec) mysql> desc departments; +----------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+-------+ | dep_id | int(4) | YES | | NULL | | | dep_name | varchar(11) | YES | | NULL | | +----------+-------------+------+-----+---------+-------+ rows in set (0.00 sec) # 创建外键不成功 mysql> create table staff_info (s_id int,name varchar(20),dep_id int,foreign key(dep_id) references departments(dep_id)); ERROR 1215 (HY000): Cannot add foreign key # 设置dep_id非空,仍然不能成功创建外键 mysql> alter table departments modify dep_id int(4) not null; Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc departments; +----------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+-------+ | dep_id | int(4) | NO | | NULL | | | dep_name | varchar(11) | YES | | NULL | | +----------+-------------+------+-----+---------+-------+ rows in set (0.00 sec) mysql> create table staff_info (s_id int,name varchar(20),dep_id int,foreign key(dep_id) references departments(dep_id)); ERROR 1215 (HY000): Cannot add foreign key constraint # 当设置字段为unique唯一字段时,设置该字段为外键成功 mysql> alter table departments modify dep_id int(4) unique; Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc departments; +----------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+-------+ | dep_id | int(4) | YES | UNI | NULL | | | dep_name | varchar(11) | YES | | NULL | | +----------+-------------+------+-----+---------+-------+ rows in set (0.01 sec) mysql> create table staff_info (s_id int,name varchar(20),dep_id int,foreign key(dep_id) references departments(dep_id)); Query OK, 0 rows affected (0.02 sec)

#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 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, foreign key(dpt_id) references department(id) on delete cascade # 级连删除 on update cascade # 级连更新 )engine=innodb; #先往父表department中插入记录 insert into department values (1,'教质部'), (2,'技术部'), (3,'人力资源部'); #再往子表employee中插入记录 insert into employee values (1,'yuan',1), (2,'nezha',2), (3,'egon',2), (4,'alex',2), (5,'wusir',3), (6,'李沁洋',3), (7,'皮卡丘',3), (8,'程咬金',3), (9,'程咬银',3) ; #删父表department,子表employee中对应的记录跟着删 mysql> delete from department where id=2; Query OK, 1 row affected (0.00 sec) mysql> select * from employee; +----+-----------+--------+ | id | name | dpt_id | +----+-----------+--------+ | 1 | yuan | 1 | | 5 | wusir | 3 | | 6 | 李沁洋 | 3 | | 7 | 皮卡丘 | 3 | | 8 | 程咬金 | 3 | | 9 | 程咬银 | 3 | +----+-----------+--------+ rows in set (0.00 sec) #更新父表department,子表employee中对应的记录跟着改 mysql> update department set id=2 where id=3; Query OK, 1 row affected (0.01 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from employee; +----+-----------+--------+ | id | name | dpt_id | +----+-----------+--------+ | 1 | yuan | 1 | | 5 | wusir | 2 | | 6 | 李沁洋 | 2 | | 7 | 皮卡丘 | 2 | | 8 | 程咬金 | 2 | | 9 | 程咬银 | 2 | +----+-----------+--------+ rows in set (0.00 sec)

. cascade方式 在父表上update/delete记录时,同步update/delete掉子表的匹配记录 . set null方式 在父表上update/delete记录时,将子表上匹配记录的列设为null 要注意子表的外键列不能为not null . No action方式 如果子表中有匹配的记录,则不允许对父表对应候选键进行update/delete操作 . Restrict方式 同no action, 都是立即检查外键约束 . Set default方式 父表有变更时,子表将外键列设置成一个默认的值 但Innodb不能识别
总结:
# 什么是约束 # not null 不能为空的 # unique 唯一 = 不能重复 # primary key 主键 = 不能为空 且 不能重复 # foreign key 外键约束 # 为什么要约束 # 是因为一个表中的数据要想完整规范,就必须对一些字段有基础的约束 # 一般情况下,我们都会根据程序的需求个特点对数据库进行约束 # 在你的开发生涯中,你应该对数据有一个基础的判断 # 在mysql中不区分大小写 # 一个关键字 :NULL null关键字 表示 空(相当于PYTHON中的None) # 创建表 # create table 表名 (字段名 数据类型(宽度) 约束条件,) # 约束一 not null # create table t (id int not null, # sex enum('male','female') not null default 'male') # 约束二 unique 唯一,允许多个字段为null # 设置某一个字段的内容必须是唯一的 # create table t3 (id int unique); # 你设置了唯一,就不能插入两个相同的内容 测试:除了null之外 # create table t3 (id int not null unique); # 你设置了唯一+非空,就不能插入两个相同的内容,也不能插入NULL,就相当于设置了一个主键primary key # create table t3 (id int, name char(12), unique(id),unique(name)); # create table t4 (pid int, pname char(12),ip char(15),port int,unique(ip,port)); # create table t4 (pid int, pname char(12), # ip char(15) not null, # port int not null , # unique(ip,port)); # 记录每一个程序的信息 # pid 程序名 ip地址 端口号 # 111 pycharm # 123 pycharm # 234 mysqld 192.168.11.44 3306 # 234 mysqld 192.168.11.22 3306 # 235 kugou 192.168.11.44 8000 # 两个或者多个字段的内容 = 联合唯一 # 约束三 # 主键 每一张表只能有一个主键 # primary key = not null + unique # create table t5 (id int primary key); # 能设置多个主键么 ? 不能 # create table t5 (id int primary key,name char(12) primary key); # 这样直接的报错 # 能不能设置多个非空 + 唯一 ? 能 # create table t6 (id int not null unique,name char(12) not null unique); # 但是第二个会自动的编程唯一的 # 联合主键 # create table t7 (pid int, pname char(12), # ip char(15), # port int, # primary key(ip,port)); # auto_increment 自增 # create table t8 (id int unique auto_increment,name char(12)); # create table t9 (id int primary key auto_increment,name char(12)); # 对于自增id来说,删除数据并不会影响自增 # 设置为自增,用户最好不要自己插入这个字段 # 约束四 外键 # 部门id 部门名称 部门办公室号 # create table department (id int unique,dep_name char(20),dep_num int); # alter table department modify id int unique; # 员工id name 年龄 工资 部门id(外键) # create table employee (id int,name char(12),age int,salary int,dep_id int, # foreign key(dep_id) references department(id)); # insert into department (id,dep_name) values # (1,'教质部'), # (2,'技术部'), # (3,'人力资源部'); # 如果添加了外键约束,外键是employee(dep_id),那么employee(dep_id)和department (ide)都会受到约束 # update department set id = 3 where id = 2; # create table employee2 (id int,name char(12),age int,salary int,dep_id int, # foreign key(dep_id) references department(id) on delete cascade on update cascade ); # insert into department (id,dep_name) values # (3,'人力资源部'); # # insert into employee2 (id,name,dep_id) values # (1,'yuan',1), # (2,'nezha',2), # (3,'egon',2), # (4,'alex',2), # (5,'wusir',3), # (6,'李沁洋',3), # (7,'皮卡丘',3), # (8,'程咬金',3), # (9,'程咬银',3) # ; # 约束 4个 # not null # 不允许为空 # default # 设置默认值 # unique # 唯一,不能约束null # 联合唯一 # auto_increment # 自增 必须在表中是一个主键,至少是一个unique,对于id来说,删除数据并不会影响自增
# primary key # 主键 = not null + unique (同一张表不能有两个主键) # 联合主键 # foreign key # 本表中的字段关联另一张表中的"唯一"字段 ,本表中的字段是 外键,外表中的字段必须唯一/主键 # create table 表名 ( # 字段名1 字段类型(宽度) not null default 默认值, # 字段名2 字段类型(宽度) not null unique, # 字段名3 字段类型(宽度) primary key, # 字段名4 int(宽度) unique auto_increment, # ) # create table 表名 ( # 字段名1 字段类型(宽度) not null, # 字段名2 字段类型(宽度) not null, # 字段名3 字段类型(宽度), # 字段名4 int(宽度), # unique(字段名2), # primary key(字段名3), # unique(字段名4) auto increment, # ) # create table 表名 ( # 字段名1 字段类型(宽度) not null, # 字段名2 字段类型(宽度) not null, # 字段名3 字段类型(宽度), # 字段名4 int(宽度) auto increment, # unique(字段名1,字段名2), # primary key(字段名3,字段名4), # ); # create table 表名( # 字段名1 字段类型(宽度) not null, # 字段名2 字段类型(宽度) not null, # 外键名 字段类型(宽度), # foreign key (外建) references 外表(外表中的字段) # on delete cascade # on update cascade, # primary key(字段名1) # ) # 添加主键 # alter table 表名 modify 字段名 类型(宽度) primary key; # +--------------------+-------------+---------------------+ # | 名字 | 年龄 | 月薪 | # +--------------------+-------------+---------------------+ # | 姓名 ; egon | 薪资 : 18 | 薪资 : 7300.33 | # | 姓名 ; alex | 薪资 : 78 | 薪资 : 1000000.31 | # | 姓名 ; wupeiqi | 薪资 : 81 | 薪资 : 8300.00 | # | 姓名 ; yuanhao | 薪资 : 73 | 薪资 : 3500.00 | # | 姓名 ; liwenzhou | 薪资 : 28 | 薪资 : 2100.00 | # | 姓名 ; 歪歪 | 薪资 : 48 | 薪资 : 3000.13 | # | 姓名 ; 丫丫 | 薪资 : 38 | 薪资 : 2000.35 | # | 姓名 ; 丁丁 | 薪资 : 18 | 薪资 : 1000.37 | # | 姓名 ; 星星 | 薪资 : 18 | 薪资 : 3000.29 | # | 姓名 ; 格格 | 薪资 : 28 | 薪资 : 4000.33 | # | 姓名 ; 张野 | 薪资 : 28 | 薪资 : 10000.13 | # | 姓名 ; 程咬金 | 薪资 : 18 | 薪资 : 20000.00 | # | 姓名 ; 程咬银 | 薪资 : 18 | 薪资 : 19000.00 | # | 姓名 ; 程咬铜 | 薪资 : 18 | 薪资 : 18000.00 | # | 姓名 ; 程咬铁 | 薪资 : 18 | 薪资 : 17000.00 | # +--------------------+-------------+---------------------+
外键的例子:
# 班级表 create table class(cid int auto_increment,caption char(32) not null,primary key(cid)); insert into class values(1,'三年二班'),(2,'一年三班'),(3,'三年一班') insert into class values(2,'一年三班') insert into class values(3,'三年一班') # 学生表 create table student(sid int primary key auto_increment,sname char(32) not null,gender enum('女','男') default '女',class_id int not null,foreign key(class_id) references class(cid) on delete cascade on update cascade); insert into student values(1,'钢弹','女',1),(2,'铁锤','女',1),(3,'山炮','男',2); # insert into student values(2,'铁锤','女',1); # insert into student values(3,'山炮','男',2); #老师表 create table teacher(tid int auto_increment,tname char(32) not null,primary key(tid)); insert into teacher values(1,'波多'),(2,'苍空'),(3,'饭岛'); # insert into teacher values(1,'苍空'); # insert into teacher values(1,'饭岛'); #课程表 create table course(cid int primary key auto_increment,cname char(32) not null,tearch_id int not null,foreign key(tearch_id) references teacher(tid) on delete cascade on update cascade); insert into course values(1,'生物',1),(2,'体育',1),(3,'物理',2); # insert into course values(1,'体育',1); # insert into course values(1,'物理',2); #成绩表 create table score (sid int primary key auto_increment,student_id int not null,corse_id int not null,number int not null,foreign key(student_id) references student(sid) on delete cascade on update cascade,foreign key(corse_id) references course(cid) on delete cascade on update cascade); insert into score values(1,1,1,60),(2,1,2,59),(3,2,2,100); # insert into score values(2,1,2,59); # insert into score values(3,2,2,100); create table score1 (sid int primary key auto_increment,student_id int unique,corse_id int not null,number int not null,foreign key(student_id) references student(sid) on delete cascade on update cascade,foreign key(corse_id) references course(cid) on delete cascade on update cascade); insert into score1 values(1,1,1,60),(2,1,2,59),(3,2,2,100);