mysql表操作2

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),
      constraint pk_name 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)
  
      单列主键

• 多列主键

    ==================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)

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

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

• 实例代码

#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,
constraint fk_name foreign key(dpt_id)
references department(id)
on delete cascade
on 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),

#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 |
+----+-------+--------+

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

• 一对多关系

  =====================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 cascade
  on 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)
  ;

• 多对多关系

  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 cascade
  on update cascade,
  constraint fk_book foreign key(book_id) references book(id)
  on delete cascade
  on 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)
  ;

• 一一对应的关系

#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,
qq varchar(10) not null,
phone char(16) not null
);


create table student(
id int primary key auto_increment,
class_name varchar(20) not null,
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unique
on delete cascade
on update cascade
);


#增加客户
insert into customer(name,qq,phone) values
(‘李飞机‘,‘31811231‘,13811341220),
(‘王大炮‘,‘123123123‘,15213146809),
(‘守榴弹‘,‘283818181‘,1867141331),
(‘吴坦克‘,‘283818181‘,1851143312),
(‘赢火箭‘,‘888818181‘,1861243314),
(‘战地雷‘,‘112312312‘,18811431230)
;


#增加学生
insert into student(class_name,customer_id) values
(‘脱产3班‘,3),
(‘周末19期‘,4),
(‘周末19期‘,5)
;

修改表

语法：
1. 修改表名
      ALTER TABLE 表名 
                          RENAME 新表名;

2. 增加字段
      ALTER TABLE 表名
                          ADD 字段名  数据类型 [完整性约束条件…],
                          ADD 字段名  数据类型 [完整性约束条件…];
      ALTER TABLE 表名
                          ADD 字段名  数据类型 [完整性约束条件…]  FIRST;
      ALTER TABLE 表名
                          ADD 字段名  数据类型 [完整性约束条件…]  AFTER 字段名;
                            
3. 删除字段
      ALTER TABLE 表名 
                          DROP 字段名;

4. 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…];

mysql表操作2

标签：com   介绍   解决   res   har   修改表   into   one   span