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)
