今天在测试UDF提权时，发现一个令人蛋疼的BUG。

正常在导入UDF.dll后，直接创建函数即可。

mysql> create function sys_eval returns string soname "udf.dll";
Query OK, 0 rows affected (0.00 sec)mysql> select * from mysql.func;
+----------+-----+---------+----------+
| name     | ret | dl      | type     |
+----------+-----+---------+----------+
| sys_eval |   0 | udf.dll | function |
+----------+-----+---------+----------+
1 row in set (0.00 sec)

删除可以使用drop function或者delete from，先用drop function删除一次

mysql> drop function sys_eval;
Query OK, 0 rows affected (0.02 sec)mysql> select * from mysql.func;
Empty set (0.00 sec)

再次创建也可以成功的

mysql> create function sys_eval returns string soname "udf.dll";
Query OK, 0 rows affected (0.00 sec)mysql> select * from mysql.func;
+----------+-----+---------+----------+
| name     | ret | dl      | type     |
+----------+-----+---------+----------+
| sys_eval |   0 | udf.dll | function |
+----------+-----+---------+----------+
1 row in set (0.00 sec)

再拿delete from mysql.func where name='sys_eval'来删除，就会发现创建不成功了，有如下提示

mysql> create function sys_eval returns string soname "udf.dll";
Query OK, 0 rows affected (0.02 sec)mysql> delete from mysql.func where name='sys_eval';
Query OK, 1 row affected (0.01 sec)mysql> create function sys_eval returns string soname "udf.dll";
ERROR 1125 (HY000): Function 'sys_eval' already existsmysql> select * from mysql.func;
Empty set (0.00 sec)

看来只能使用drop关键字来删除，暂时没有好的解决这个问题的办法。