mysql中刪除用戶權限

revoke:只刪除了用戶權限，但沒有刪除這個用戶
mysql> select user,host from user;
+------------------+-----------+
| user             | host      |
+------------------+-----------+
| root             | 127.0.0.1 |
| debian-sys-maint | localhost |
| root             | localhost |
| xbb              | localhost |
| root             | wangxg    |
+------------------+-----------+
mysql> revoke insert,update,delete,select ON *.* from 'xbb'@'localhost' IDENTIFIED BY '123';

mysql> select user,host from user;
+------------------+-----------+
| user             | host      |
+------------------+-----------+
| root             | 127.0.0.1 |
| debian-sys-maint | localhost |
| root             | localhost |
| xbb              | localhost |
| root             | wangxg    |
+------------------+-----------+
5 rows in set (0.00 sec)

mysql> show grants for xbb@localhost ;
+------------------------------------------------------------------------------------------------------------+
| Grants for xbb@localhost                                                                                   |
+------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'xbb'@'localhost' IDENTIFIED BY PASSWORD '*23AE809DDACAF96AF0FD78ED04B6A265E05AA257' |
+------------------------------------------------------------------------------------------------------------+

drop user:刪除了整個用戶及其權限（包括數據字典中的數據）
mysql> drop user 'xbb'@'localhost';
Query OK, 0 rows affected (0.00 sec)

mysql> select user,host from user;
+------------------+-----------+
| user             | host      |
+------------------+-----------+
| root             | 127.0.0.1 |
| debian-sys-maint | localhost |
| root             | localhost |
| root             | wangxg    |
+------------------+-----------+
4 rows in set (0.00 sec)

delete from user:刪除了mysql庫中某一用戶，（但不能刪除數據字典【information_schema】中相關的記錄）
mysql> GRANT insert,update,delete,select ON *.* TO 'xbb'@'localhost' IDENTIFIED BY '123';
Query OK, 0 rows affected (0.00 sec)

mysql> select user,host from user;
+------------------+-----------+
| user             | host      |
+------------------+-----------+
| root             | 127.0.0.1 |
| debian-sys-maint | localhost |
| root             | localhost |
| xbb              | localhost |
| root             | wangxg    |
+------------------+-----------+
5 rows in set (0.00 sec)

mysql> delect * from user where user ='xbb';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'delect * from user where user ='xbb'' at line 1
mysql> delete * from user where user ='xbb';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '* from user where user ='xbb'' at line 1
mysql> delete  from user where user ='xbb';
Query OK, 1 row affected (0.09 sec)

mysql> select user,host from user;
+------------------+-----------+
| user             | host      |
+------------------+-----------+
| root             | 127.0.0.1 |
| debian-sys-maint | localhost |
| root             | localhost |
| root             | wangxg    |
+------------------+-----------+
4 rows in set (0.00 sec)