mysql如何增加字段

mysql增加两个字段：

（推荐教程：mysql视频教程）

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)

mysql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