revoke:只删除了用户权限，但没有删除这个用户

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:删除了整个用户及其权限（包括数据字典中的数据）

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:删除了mysql库中某一用户，（但不能删除数据字典【information_schema】中相关的记录）

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)