mysql两列想减负数显示问题

Question

mysql> select idd-id,id,idd,name from test order by 1 desc ;
+----------------------+------+-----+------+
| idd-id | id | idd | name |
+----------------------+------+-----+------+
| 18446744073709551614 | 10 | 8 | |  
| 199 | 1 | 200 | |  
| 46 | 4 | 50 | |  
| 37 | 3 | 40 | |  
| 28 | 2 | 30 | |  
| 1 | 1 | 2 | |  
+----------------------+------+-----+------+
为什么不是负数？？？

Answer 1

mysql> select * from test;
+------+-----+------+
| id   | idd | name |
+------+-----+------+
|    1 | 200 |      | 
|    2 |  30 |      | 
|    3 |  40 |      | 
|    4 |  50 |      | 
|    1 |   2 |      | 
|   10 |   8 |      | 
|   -1 |   0 |      | 
| NULL |   0 |      | 
+------+-----+------+
8 rows in set (0.00 sec)mysql> select id-idd from test;
+----------------------+
| id-idd               |
+----------------------+
|                 NULL | 
| 18446744073709551615 | 
| 18446744073709551615 | 
|                    2 | 
| 18446744073709551588 | 
| 18446744073709551579 | 
| 18446744073709551570 | 
| 18446744073709551417 | 
+----------------------+
8 rows in set (0.00 sec)mysql> 

Answer 2

mysql> show create table test;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                               |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test  | CREATE TABLE `test` (
  `id` int(11) default NULL,
  `idd` int(10) unsigned NOT NULL,
  `name` mediumtext NOT NULL,
  KEY `id` (`id`),
  KEY `idd` (`idd`),
  KEY `idd_2` (`idd`,`id`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk | 
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)mysql> 是那个unsigned引起的么？？？？？？？？

Answer 3

测试，确实是unsigned引起的，去掉后，
结果正常