mysql和oracle一样也是有数据字典表的，是存在单独的一个库叫INFORMATION_SCHEMA，要查看某张表的外键要从字典表中查找
如mysql查询某张表的外键，可以用下面的方式查询
use INFORMATION_SCHEMA;
select TABLE_NAME,COLUMN_NAME,CONSTRAINT_NAME,REFERENCED_TABLE_NAME,REFERENCED_COLUMN_NAME from KEY_COLUMN_USAGE where table_name = ‘logistics_member_express‘;
+--------------------------+-----------------+----------------------------+------------------------+------------------------+
| TABLE_NAME | COLUMN_NAME | CONSTRAINT_NAME | REFERENCED_TABLE_NAME | REFERENCED_COLUMN_NAME |
+--------------------------+-----------------+----------------------------+------------------------+------------------------+
| logistics_member_express | id | PRIMARY | NULL | NULL |
| logistics_member_express | express_user_id | Reflogistics_express_user6 | logistics_express_user | id |
+--------------------------+-----------------+----------------------------+------------------------+------------------------+
2 rows in set (0.00 sec)
如果某个外键不要的话就可以删除啦：
ALTER TABLE logistics_member_express DROP FOREIGN KEY Reflogistics_express_user6;