MySQL 数据表中添加字段

目录

添加字段

将添加的字段放在表中的第一行

将新增的字段放在指定字段之后

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在一个创建好的表中添加字段。

 

添加字段

alter table  add column   ; 
  
 
   
 
    
 
     
table name
 
     
要添加字段的表名称
 
    
 
    
 
     
column name
 
     
要添加的字段名称
 
    
 
    
 
     
column type
 
     
要添加字段的类型
 
    
 
   
 
  
 
  
例如对user表添加一个字段name用来记录用户的名称：
 
  
mysql> desc user;
+-------+------------------------------+------+-----+---------+-------+
| Field | Type                         | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+-------+
| phone | char(11)                     | NO   | PRI | NULL    |       |
| email | varchar(255)                 | YES  |     | NULL    |       |
| age   | tinyint(3) unsigned          | YES  |     | NULL    |       |
| level | set('0','1','2','3','4','5') | YES  |     | NULL    |       |
+-------+------------------------------+------+-----+---------+-------+
4 rows in set (0.02 sec)

mysql> alter table user add column name varchar(255) not null;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+-------+------------------------------+------+-----+---------+-------+
| Field | Type                         | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+-------+
| phone | char(11)                     | NO   | PRI | NULL    |       |
| email | varchar(255)                 | YES  |     | NULL    |       |
| age   | tinyint(3) unsigned          | YES  |     | NULL    |       |
| level | set('0','1','2','3','4','5') | YES  |     | NULL    |       |
| name  | varchar(255)                 | NO   |     | NULL    |       |
+-------+------------------------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
 
  
提示：默认新增字段命令将新增的字段放在表的最后一行。
 
  
 
 
  
将添加的字段放在表中的第一行
 
  
alter table  add column   first; 
  
 
   
 
    
 
     
table name
 
     
要添加字段的表名称
 
    
 
    
 
     
column name
 
     
要添加的字段名称
 
    
 
    
 
     
column type
 
     
要添加字段的类型
 
    
 
   
 
  
 
  
例如要对user表添加一个字段 username用来记录用户的昵称：
 
  
mysql> desc user;
+-------+------------------------------+------+-----+---------+-------+
| Field | Type                         | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+-------+
| phone | char(11)                     | NO   | PRI | NULL    |       |
| email | varchar(255)                 | YES  |     | NULL    |       |
| age   | tinyint(3) unsigned          | YES  |     | NULL    |       |
| level | set('0','1','2','3','4','5') | YES  |     | NULL    |       |
| name  | varchar(255)                 | NO   |     | NULL    |       |
+-------+------------------------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> alter table user add column username varchar(200) not null first;
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+----------+------------------------------+------+-----+---------+-------+
| Field    | Type                         | Null | Key | Default | Extra |
+----------+------------------------------+------+-----+---------+-------+
| username | varchar(200)                 | NO   |     | NULL    |       |
| phone    | char(11)                     | NO   | PRI | NULL    |       |
| email    | varchar(255)                 | YES  |     | NULL    |       |
| age      | tinyint(3) unsigned          | YES  |     | NULL    |       |
| level    | set('0','1','2','3','4','5') | YES  |     | NULL    |       |
| name     | varchar(255)                 | NO   |     | NULL    |       |
+----------+------------------------------+------+-----+---------+-------+
6 rows in set (0.01 sec)
 
  
 
 
  
将新增的字段放在指定字段之后
 
  
alter table  add column   after ; 
  
 
   
 
    
 
     
table name
 
     
要添加字段的表名称
 
    
 
    
 
     
column name
 
     
要添加的字段名称
 
    
 
    
 
     
column type
 
     
要添加字段的类型
 
    
 
    
 
     
old_param
 
     
要将新字段放入某个旧字段之后
 
    
 
   
 
  
 
  
例如要对user表添加一个字段 sex用来记录用户的性别，并将sex放入level之后：
 
  
mysql> desc user;
+-------+------------------------------+------+-----+---------+-------+
| Field | Type                         | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+-------+
| uuid  | char(36)                     | NO   | PRI | NULL    |       |
| phone | char(11)                     | NO   | UNI | NULL    |       |
| email | varchar(255)                 | YES  | MUL | NULL    |       |
| age   | tinyint(3) unsigned          | YES  |     | NULL    |       |
| level | set('0','1','2','3','4','5') | YES  |     | NULL    |       |
+-------+------------------------------+------+-----+---------+-------+
5 rows in set (0.01 sec)

mysql> alter table user add column sex enum('boy', 'girl') after level;
Query OK, 0 rows affected (0.10 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+-------+------------------------------+------+-----+---------+-------+
| Field | Type                         | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+-------+
| uuid  | char(36)                     | NO   | PRI | NULL    |       |
| phone | char(11)                     | NO   | UNI | NULL    |       |
| email | varchar(255)                 | YES  | MUL | NULL    |       |
| age   | tinyint(3) unsigned          | YES  |     | NULL    |       |
| level | set('0','1','2','3','4','5') | YES  |     | NULL    |       |
| sex   | enum('boy','girl')           | YES  |     | NULL    |       |
+-------+------------------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)