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

http://blog.csdn.net/qustdjx/article/details/8875827