数据库在指定位置增加字段

数据库教程在指定位置增加字段
mysql教程> -- 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>