题目如下：
Num
1
2
4
6
7
8
10
11
13
写条SQL语句转成下表：
Column1 Column2
1 2
4 4
6 8
10 11
13 13
答案：
select MIN(Num),MAX(Num) from
(select ROW_NUMBER() over (order by Num) rk, Num From Numbers) A
Group by (A.rk - A.Num)
order by Min(Num)
