一 表于表之间的关联
foregin key：设置外键表于表之间建立关联。
多对一关联：
创建步骤，应该先创建好被关联的那一张表，然后再去创建关联的那一张表。
关联表的多条对应着被关联的那张表的一条记录，而被关联的那一张表的多条记录不能对于着关联表的一条记录。属于单向关联
一对一关联：
创建步骤：还是先创建被关联的那一张表，然后在去创建关联的那一张表。
在多对一的基础上加上一条唯一的约束，关联表只能对应被关联表的一条记录。被关联表也只能对于关联表的一条记录
多对多关联：
创建步骤：首先先要创建出两张需要关联的表，然后在用第三张表将它们关联起来
关联表的多条记录对应着被关联表的一条记录，而被关联表的多条记录也同时对应着关联表的一条记录。
foregin key(关联的字段1) references 需要关联的那张表表名（关联的字段2）：表名后面加的一般都是表的主键。
使用的好处是：限制了关联表的外键的传入的值，只能在被关联表的主键范围内。
坏处是：如果被关联表的主键关联上关联表的外键，就不能随便的删除和修改表关联表里面的数据。
解决方案1：先将关联表相对应的记录给删除掉，这样才能够对被关联表进行删除和修改。这样做是非常麻烦的，以为不知到有多少条记录相对应，这样删除的话是非常麻烦的，不建议用。
解决方案2：在关联上被关联表之后，后面加上：
on delete cascade：如果被关联表的该条数据删除掉，那么关联表与该记录相对应的记录也会变删除。
on update cascade：如果被关联表的该条数据被修改，那么关联表与该记录相对应的记录也会被修改。
#先创建被关联的表
create table dep(
id int primary key auto_increment,
dep_name char(20) not null unique,
dep_comment varchar(50)
)auto_increment=200;
insert into dep(dep_name,dep_comment) values
('IT','xxxxxxxxxx'),
('Sale','yhyyyyyyy'),
('Operation','asdfadfadsf'),
('HR','asfasdfasdfasdfasdf')
;
#再创表去关联上面的表
create table emp(
id int primary key auto_increment,
name char(6) not null,
sex enum('male','female') not null default 'male',
dep_id int,
foreign key(dep_id) references dep(id)
on delete cascade
on update cascade
);
insert into emp(name,sex,dep_id) values
('egon','male',200),
('alex','male',200),
('yh','female',203),
('evia','female',200),
('wpq','male',202)
;
insert into emp(name,sex,dep_id) values
('alex1','male',250);
#解散一个部门
#未指定同步更新、同步删除的参数时，需要这么删除
delete from emp where dep_id=200;
delete from dep where id=200;
#指定后
mysql> select * from dep;
+-----+-----------+---------------------+
| id | dep_name | dep_comment |
+-----+-----------+---------------------+
| 200 | IT | xxxxxxxxxx |
| 201 | Sale | yhyyyyyyy |
| 202 | Operation | asdfadfadsf |
| 203 | HR | asfasdfasdfasdfasdf |
+-----+-----------+---------------------+
4 rows in set (0.00 sec)
mysql> select * from emp;
+----+------+--------+--------+
| id | name | sex | dep_id |
+----+------+--------+--------+
| 1 | egon | male | 200 |
| 2 | alex | male | 200 |
| 3 | yh | female | 203 |
| 4 | evia | female | 200 |
| 5 | wpq | male | 202 |
+----+------+--------+--------+
5 rows in set (0.00 sec)
mysql> delete from dep where id=200;
Query OK, 1 row affected (0.06 sec)
mysql> select * from emp;
+----+------+--------+--------+
| id | name | sex | dep_id |
+----+------+--------+--------+
| 3 | yh | female | 203 |
| 5 | wpq | male | 202 |
+----+------+--------+--------+
2 rows in set (0.00 sec)
mysql> select * from dep;
+-----+-----------+---------------------+
| id | dep_name | dep_comment |
+-----+-----------+---------------------+
| 201 | Sale | yhyyyyyyy |
| 202 | Operation | asdfadfadsf |
| 203 | HR | asfasdfasdfasdfasdf |
+-----+-----------+---------------------+
3 rows in set (0.00 sec)
mysql> select * from emp;
+----+------+--------+--------+
| id | name | sex | dep_id |
+----+------+--------+--------+
| 3 | yh | female | 203 |
| 5 | wpq | male | 202 |
+----+------+--------+--------+
2 rows in set (0.00 sec)
mysql> update dep set id=2002 where id=202;
Query OK, 1 row affected (0.06 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from dep;
+------+-----------+---------------------+
| id | dep_name | dep_comment |
+------+-----------+---------------------+
| 201 | Sale | yhyyyyyyy |
| 203 | HR | asfasdfasdfasdfasdf |
| 2002 | Operation | asdfadfadsf |
+------+-----------+---------------------+
3 rows in set (0.00 sec)
mysql> select * from emp;
+----+------+--------+--------+
| id | name | sex | dep_id |
+----+------+--------+--------+
| 3 | yh | female | 203 |
| 5 | wpq | male | 2002 |
+----+------+--------+--------+
2 rows in set (0.00 sec)
#多对多的创建方法：
mysql> use DAY43;
Database changed
mysql> CREATe table user_1(id int primary key auto_increment,
-> name char(10) not null,
-> password char(30) not null);
Query OK, 0 rows affected (0.28 sec)
mysql>
mysql> insert into user_1(name,password) values('fang','dsads454234'),
-> ('jie','dsfsfd65465'),
-> ('yi','dfsdf43543'),
-> ('dong','dsfdsh5445');
Query OK, 4 rows affected (0.04 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql>
mysql> create table role_1(id int PRIMARY key auto_increment,
-> name char(10) not null,
-> quanxian char(3) not null);
Query OK, 0 rows affected (0.25 sec)
mysql>
mysql> insert into role_1(name,quanxian)values('gl','rwx'),('r1','rw'),('r2','rx'),('r3','r');
Query OK, 4 rows affected (0.02 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql>
mysql> create table user_role_1(id int primary key auto_increment,
-> user_id int,
-> foreign key(user_id) references user(id)
-> on update cascade on delete CASCADE ,
-> role_id int,
-> foreign key(role_id) references role(id)
-> on UPDATE cascade on delete CASCADE);
Query OK, 0 rows affected (0.24 sec)
mysql>
mysql>
mysql> insert into user_role(user_id,role_id)values(1,1),(1,2),(1,4),(2,3),(2,4),(3,2),(3,4),(4,1);
Query OK, 8 rows affected (0.10 sec)
Records: 8 Duplicates: 0 Warnings: 0
mysql>
mysql>
mysql> SELECT * from user_1;
+----+------+-------------+
| id | name | password |
+----+------+-------------+
| 1 | fang | dsads454234 |
| 3 | jie | dsfsfd65465 |
| 5 | yi | dfsdf43543 |
| 7 | dong | dsfdsh5445 |
+----+------+-------------+
4 rows in set (0.00 sec)
mysql> SELECT * from role_1;
+----+------+----------+
| id | name | quanxian |
+----+------+----------+
| 1 | gl | rwx |
| 3 | r1 | rw |
| 5 | r2 | rx |
| 7 | r3 | r |
+----+------+----------+
4 rows in set (0.00 sec)
mysql> SELECT * from user_role_1;
Empty set (0.00 sec)
mysql> desc user_role_1;
+---------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| user_id | int(11) | YES | MUL | NULL | |
| role_id | int(11) | YES | MUL | NULL | |
+---------+---------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> show create table user_role_1;
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| user_role_1 | CREATE TABLE `user_role_1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) DEFAULT NULL,
`role_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `user_id` (`user_id`),
KEY `role_id` (`role_id`),
CONSTRAINT `user_role_1_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `user_role_1_ibfk_2` FOREIGN KEY (`role_id`) REFERENCES `role` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
一对一的创建方法：
mysql> use day43;
Database changed
mysql> create table customer_1(id int primary key auto_increment,
-> name char(10) not null,
-> phone char(12) not null unique,
-> qq char(10) UNIQUE);
Query OK, 0 rows affected (0.33 sec)
mysql>
mysql>
mysql> insert into customer_1(name,phone,qq)values('fang','15435789257','1343578983'),
-> ('yan','15578983325','4357898332'),
-> ('dong','14757898337','475785832'),
-> ('jie','1557858857','57875782'),
-> ('lei','1555785257','78525783'),
-> ('yi','15590034557','13468550'),
-> ('haiyan','1853387597','65442365'),
-> ('hui','15934233557','932923743'),
-> ('jia','15256784455','426557824');
Query OK, 9 rows affected (0.05 sec)
Records: 9 Duplicates: 0 Warnings: 0
mysql>
mysql> create table student_1(id int primary key auto_increment,
-> name char(10) not null,
-> age int not null,
-> sex enum('male','female') not null default 'male',
-> c_id int,foreign key(c_id) references customer(id)
-> on update cascade on delete cascade);
Query OK, 0 rows affected (0.23 sec)
mysql>
mysql>
mysql> insert into student_1(name,age,sex,c_id)VALUES('fang',18,'male',1),
-> ('hui',17,'female',8),
-> ('dong',22,'male',3),
-> ('yan',20,'female',2),
-> ('haiyan',18,'female',7),
-> ('jie',21,'male',4),
-> ('lei',21,'male',5),
-> ('jia',19,'female',8);
Query OK, 8 rows affected (0.03 sec)
Records: 8 Duplicates: 0 Warnings: 0
mysql>
mysql> SELECT * from customer_1;
+----+--------+-------------+------------+
| id | name | phone | qq |
+----+--------+-------------+------------+
| 1 | fang | 15435789257 | 1343578983 |
| 3 | yan | 15578983325 | 4357898332 |
| 5 | dong | 14757898337 | 475785832 |
| 7 | jie | 1557858857 | 57875782 |
| 9 | lei | 1555785257 | 78525783 |
| 11 | yi | 15590034557 | 13468550 |
| 13 | haiyan | 1853387597 | 65442365 |
| 15 | hui | 15934233557 | 932923743 |
| 17 | jia | 15256784455 | 426557824 |
+----+--------+-------------+------------+
9 rows in set (0.00 sec)
mysql> SELECT * from student_1;
+----+--------+-----+--------+------+
| id | name | age | sex | c_id |
+----+--------+-----+--------+------+
| 1 | fang | 18 | male | 1 |
| 3 | hui | 17 | female | 8 |
| 5 | dong | 22 | male | 3 |
| 7 | yan | 20 | female | 2 |
| 9 | haiyan | 18 | female | 7 |
| 11 | jie | 21 | male | 4 |
| 13 | lei | 21 | male | 5 |
| 15 | jia | 19 | female | 8 |
+----+--------+-----+--------+------+
8 rows in set (0.00 sec)
mysql> show CREATE TABLE student_1;
+-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student_1 | CREATE TABLE `student_1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` char(10) NOT NULL,
`age` int(11) NOT NULL,
`sex` enum('male','female') NOT NULL DEFAULT 'male',
`c_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `c_id` (`c_id`),
CONSTRAINT `student_1_ibfk_1` FOREIGN KEY (`c_id`) REFERENCES `customer` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8 |
+-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
二 表的操作
alter table 表名 rename 新表名：修改一个表名。
mysql> alter table t1 rename yi; Query OK, 0 rows affected mysql> show tables; +-----------------+ | Tables_in_day43 | +-----------------+ | customer | | customer_1 | | role | | role_1 | | student | | student_1 | | user | | user_1 | | user_role | | user_role_1 | | yi | +-----------------+ 11 rows in set
增减字段：
alter table 表名 add 字段 数据类型[约束条件]，add 字段 数据类型[约束条件]； ：同时添加几个字段
alter table 表名 add 字段 数据类型[约束条件] first； #将字段添加到第一个位置
alter table 表名 add 字段 数据类型[约束条件] after 字段名； ：将字段添加到耨个字段的前面
mysql> create table t1(name char(5)); Query OK, 0 rows affected mysql> alter table t1 add age int(3),add sex char(6); Query OK, 0 rows affected Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table t1; +-------+-----------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------+-----------------------------------------------------------------------------------------------------------------------------------------------+ | t1 | CREATE TABLE `t1` ( `name` char(5) DEFAULT NULL, `age` int(3) DEFAULT NULL, `sex` char(6) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | +-------+-----------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set mysql> alter table t1 add id int primary key auto_increment first; Query OK, 0 rows affected Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table t1 add class char(6) after age; Query OK, 0 rows affected Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table t1; +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | t1 | CREATE TABLE `t1` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` char(5) DEFAULT NULL, `age` int(3) DEFAULT NULL, `class` char(6) DEFAULT NULL, `sex` char(6) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set
删除字段：
alter table 表名 drop 字段名；
| t1 | CREATE TABLE `t1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` char(5) DEFAULT NULL,
`age` int(3) DEFAULT NULL,
`class` char(6) DEFAULT NULL,
`sex` char(6) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set
mysql> alter table t1 drop
-> class;
Query OK, 0 rows affected
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table t1;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1 | CREATE TABLE `t1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` char(5) DEFAULT NULL,
`age` int(3) DEFAULT NULL,
`sex` char(6) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set
修改字段
ALTER TABLE 表名 MODIFY 字段名 数据类型 [完整性约束条件…];
ALTER TABLE 表名 CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…];
ALTER TABLE 表名 CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…];
三 表的复制
create table 新的表名 select * from 旧表名； ：复制表的结构和记录
create table 新的表名 select 字段名。。。 from 旧表名； ：复制表结构和某些记录
create table 新的表名 select * from 旧表名 where 不成立条件； ：不复制表的记录，只复制表的结构
复制是根据创建的新的表，里面的表结构和记录是另外一张表的查看的结果。
mysql> show create table t1;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1 | CREATE TABLE `t1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` char(5) DEFAULT NULL,
`age` int(3) DEFAULT NULL,
`sex` char(6) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set
mysql> insert into t1(name,age,sex)values('fang',18,'male'),('jie',19,'male'),('hai',17,'female'),('yan',17,'female');
Query OK, 4 rows affected
Records: 4 Duplicates: 0 Warnings: 0
mysql> create table t2 select * from t1;
Query OK, 4 rows affected
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from t2;
+----+------+-----+--------+
| id | name | age | sex |
+----+------+-----+--------+
| 1 | fang | 18 | male |
| 2 | jie | 19 | male |
| 3 | hai | 17 | female |
| 4 | yan | 17 | female |
+----+------+-----+--------+
4 rows in set
mysql> create table t3 select name,sex from t1;
Query OK, 4 rows affected
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from t3;
+------+--------+
| name | sex |
+------+--------+
| fang | male |
| jie | male |
| hai | female |
| yan | female |
+------+--------+
4 rows in set
mysql> create table t4 select * from t1 where 1=2;
Query OK, 0 rows affected
Records: 0 Duplicates: 0 Warnings: 0
mysql> select * from t4;
Empty set
mysql> show create table t4;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t4 | CREATE TABLE `t4` (
`id` int(11) NOT NULL DEFAULT '0',
`name` char(5) DEFAULT NULL,
`age` int(3) DEFAULT NULL,
`sex` char(6) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set