mysql 字段添加以及删除

mysql> select * from user;
+------+-----------+-----------+
| id   | name      | address   |
+------+-----------+-----------+
|    1 | xiaoming  | beijing   |
|    2 | xiaobai   | shandong  |
|    3 | xiaohong  | suzhou    |
|    4 | xiaohei   | changchun |
|    5 | xiaoli    | dongjing  |
|    6 | xiaohuang | meiguo    |
|    1 | xiaoming  | beijing   |
|    1 | xiaoming  | beijing   |
|    1 | xiaoming  | beijing   |
+------+-----------+-----------+
9 rows in set (0.00 sec)


mysql> alter table user add ziduan char(10) null;
Query OK, 0 rows affected (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 0


mysql> select * from user;
+------+-----------+-----------+--------+
| id   | name      | address   | ziduan |
+------+-----------+-----------+--------+
|    1 | xiaoming  | beijing   | NULL   |
|    2 | xiaobai   | shandong  | NULL   |
|    3 | xiaohong  | suzhou    | NULL   |
|    4 | xiaohei   | changchun | NULL   |
|    5 | xiaoli    | dongjing  | NULL   |
|    6 | xiaohuang | meiguo    | NULL   |
|    1 | xiaoming  | beijing   | NULL   |
|    1 | xiaoming  | beijing   | NULL   |
|    1 | xiaoming  | beijing   | NULL   |
+------+-----------+-----------+--------+
9 rows in set (0.00 sec)


mysql> alter table user drop column ziduan;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0


mysql> select * from user;
+------+-----------+-----------+
| id   | name      | address   |
+------+-----------+-----------+
|    1 | xiaoming  | beijing   |
|    2 | xiaobai   | shandong  |
|    3 | xiaohong  | suzhou    |
|    4 | xiaohei   | changchun |
|    5 | xiaoli    | dongjing  |
|    6 | xiaohuang | meiguo    |
|    1 | xiaoming  | beijing   |
|    1 | xiaoming  | beijing   |
|    1 | xiaoming  | beijing   |
+------+-----------+-----------+
9 rows in set (0.00 sec)