按日分组的rand()的MySQL顺序

Question

是否有可能在同一天内获得随机物品？

例如:

+----+---------------------+  
| id | md                  |  
+----+---------------------+  
|  1 | 2010-06-27 11:26:01 |  
|  2 | 2010-06-27 11:28:20 |  
|  3 | 2010-06-27 11:29:46 |  
|  4 | 2010-06-27 11:30:50 |  
|  5 | 2010-06-27 12:20:56 |  
|  6 | 2010-06-27 12:27:42 |  
|  7 | 2010-06-27 15:14:05 |  
|  8 | 2010-07-06 01:53:33 |  
|  9 | 2010-07-06 01:52:52 |  
+----+---------------------+  

我想在同一天内选择随机物品,但同时我想按日期desc订购.像这样的东西:

+----+---------------------+  
| id | md                  |  
+----+---------------------+  

|  8 | 2010-07-06 01:53:33 |  random block  
|  9 | 2010-07-06 01:52:52 |  

|  2 | 2010-06-27 11:28:20 |  random block  
|  4 | 2010-06-27 11:30:50 |  
|  1 | 2010-06-27 11:26:01 |  
|  6 | 2010-06-27 12:27:42 |  
|  3 | 2010-06-27 11:29:46 |  
|  5 | 2010-06-27 12:20:56 |  
|  7 | 2010-06-27 15:14:05 |  

+----+---------------------+  

不知道如何开始或者这是否可能,因为rand()的订单不接受分组.

Answer 1

真的很简单:

SELECT * 
FROM tbl 
ORDER BY md DESC, RAND()