Add and delete mysql field

MySQL> the SELECT * from the User;
 + ------ + ----------- + ----------- + 
| the above mentioned 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 the 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 the SET ( 0.00 sec)
Add and delete mysql field

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