Mysql两个查询都使用“Using where&Using temporary”,但速度有差异

我有两个问题来获取以下信息。

1. SELECT distinct(I), O from (SELECT I, O FROM HB WHERE ID > 0) as H;
   

2. SELECT distinct(I), O FROM HB WHERE ID > 0;
   

1. 1   PRIMARY <derived2>  ALL                 5   Using temporary
   2   DERIVED HB  range   PRIMARY PRIMARY 4       5   Using where
   

2. 这样地:

   1   SIMPLE  HB  range   PRIMARY PRIMARY 4       5   Using where; Using temporary
   

但是1。比2慢很多。这有什么区别?

提前谢谢。