这个本身属于MySQL的基本语法，我这里给出一个例子而已。

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mysql> -- 测试数据库在指定位置增加字段  
mysql> drop table if exists t;  
Query OK, 0 rows affected (0.06 sec)  
mysql> create table t(age int,address varchar(50));  
Query OK, 0 rows affected (0.06 sec)  
mysql> desc t;  
+---------+-------------+------+-----+---------+-------+  
| Field   | Type        | Null | Key | Default | Extra |  
+---------+-------------+------+-----+---------+-------+  
| age     | int(11)     | YES  |     | NULL    |       |  
| address | varchar(50) | YES  |     | NULL    |       |  
+---------+-------------+------+-----+---------+-------+  
2 rows in set (0.02 sec)  
mysql> alter table t add column name varchar(20) after age;  
Query OK, 0 rows affected (0.16 sec)  
Records: 0  Duplicates: 0  Warnings: 0 
mysql> desc t;  
+---------+-------------+------+-----+---------+-------+  
| Field   | Type        | Null | Key | Default | Extra |  
+---------+-------------+------+-----+---------+-------+  
| age     | int(11)     | YES  |     | NULL    |       |  
| name    | varchar(20) | YES  |     | NULL    |       |  
| address | varchar(50) | YES  |     | NULL    |       |  
+---------+-------------+------+-----+---------+-------+  
3 rows in set (0.00 sec)  
mysql> alter table t add column id int FIRST;  
Query OK, 0 rows affected (0.13 sec)  
Records: 0  Duplicates: 0  Warnings: 0 
mysql> desc t;  
+---------+-------------+------+-----+---------+-------+  
| Field   | Type        | Null | Key | Default | Extra |  
+---------+-------------+------+-----+---------+-------+  
| id      | int(11)     | YES  |     | NULL    |       |  
| age     | int(11)     | YES  |     | NULL    |       |  
| name    | varchar(20) | YES  |     | NULL    |       |  
| address | varchar(50) | YES  |     | NULL    |       |  
+---------+-------------+------+-----+---------+-------+  
4 rows in set (0.00 sec)  
mysql> 
mysql> -- 测试数据库在指定位置增加字段
mysql> drop table if exists t;
Query OK, 0 rows affected (0.06 sec)
mysql> create table t(age int,address varchar(50));
Query OK, 0 rows affected (0.06 sec)
mysql> desc t;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| age     | int(11)     | YES  |     | NULL    |       |
| address | varchar(50) | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
2 rows in set (0.02 sec)
mysql> alter table t add column name varchar(20) after age;
Query OK, 0 rows affected (0.16 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> desc t;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| age     | int(11)     | YES  |     | NULL    |       |
| name    | varchar(20) | YES  |     | NULL    |       |
| address | varchar(50) | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> alter table t add column id int FIRST;
Query OK, 0 rows affected (0.13 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> desc t;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id      | int(11)     | YES  |     | NULL    |       |
| age     | int(11)     | YES  |     | NULL    |       |
| name    | varchar(20) | YES  |     | NULL    |       |
| address | varchar(50) | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql>  

相关的语法描述为

ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name    alter_specification [, alter_specification] ...alter_specification:    table_option ...  | ADD [COLUMN] col_name column_definition        [FIRST | AFTER col_name ]