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  • MySQL中的表中增加删除字段

    1增加两个字段:

    mysql> create table id_name(id int,name varchar(20));
    Query OK, 0 rows affected (0.13 sec)
    
    
    mysql> alter table id_name add age int,add address varchar(11);
    Query OK, 0 rows affected (0.13 sec)
    Records: 0  Duplicates: 0  Warnings: 0
    
    mysql> desc id_name;
    
    +---------+-------------+------+-----+---------+-------+
    | Field   | Type        | Null | Key | Default | Extra |
    +---------+-------------+------+-----+---------+-------+
    | id      | int(11)     | YES  |     | NULL    |       |
    | name    | varchar(20) | YES  |     | NULL    |       |
    | age     | int(11)     | YES  |     | NULL    |       |
    | address | varchar(11) | YES  |     | NULL    |       |
    +---------+-------------+------+-----+---------+-------+
    4 rows in set (0.00 sec)
    
    2.删除两个字段
    mysql> alter table id_name drop column age,drop column address;
    Query OK, 0 rows affected (0.14 sec)
    Records: 0  Duplicates: 0  Warnings: 0
    
    mysql> desc id_name;
    +-------+-------------+------+-----+---------+-------+
    | Field | Type        | Null | Key | Default | Extra |
    +-------+-------------+------+-----+---------+-------+
    | id    | int(11)     | YES  |     | NULL    |       |
    | name  | varchar(20) | YES  |     | NULL    |       |
    +-------+-------------+------+-----+---------+-------+
    2 rows in set (0.00 sec)
    
    3.插入
    mysql> insert into id_name values (1,'qustdjx');
    Query OK, 1 row affected (0.00 sec)
    4.查询看一下
    mysql> alter table id_name add age int,add address varchar(11);
    Query OK, 1 row affected (0.07 sec)
    Records: 1  Duplicates: 0  Warnings: 0
    
    mysql> select * from id_name;
    +------+---------+------+---------+
    | id   | name    | age  | address |
    +------+---------+------+---------+
    |    1 | qustdjx | NULL | NULL    |
    +------+---------+------+---------+
    1 row in set (0.00 sec)
    5.新增字段并插入
    mysql> insert into id_name values(2,'qust',14,'山东');
    Query OK, 1 row affected (0.00 sec)
    
    mysql> select * from id_name;
    +------+---------+------+---------+
    | id   | name    | age  | address |
    +------+---------+------+---------+
    |    1 | qustdjx | NULL | NULL    |
    |    2 | qust    |   14 | 山东    |
    +------+---------+------+---------+
    2 rows in set (0.00 sec)
    
     
    

    1.增加一个字段
    alter table user add COLUMN new1 VARCHAR(20) DEFAULT NULL; //增加一个字段,默认为空
    alter table user add COLUMN new2 VARCHAR(20) NOT NULL;  //增加一个字段,默认不能为空  www.2cto.com  
     
    2.删除一个字段
    alter table user DROP COLUMN new2;   //删除一个字段
     
    3.修改一个字段
    alter table user MODIFY new1 VARCHAR(10);  //修改一个字段的类型
     
    alter table user CHANGE new1 new4 int;  //修改一个字段的名称,此时一定要重新指定该字段的类型

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  • 原文地址:https://www.cnblogs.com/xzlive/p/10894316.html
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