SQL窗口功能没有给我正确的输出

Question

A     B   C   D
1pm   a   1   1
2pm   a   2   2
3pm   b   1   1
4pm   b   2   2
5pm   a   3   1
6pm   a   4   2

当我做row_number() over (partition by B order by A) as C .时，得到C列。如何得到D列？

Answer 1

您需要为“相邻”值分配一个组。一种简单的方法是行号的区别：

select a, b, 
       row_number() over (partition by b, (seqnum_a - seqnum_ab) order by a) as d
from (select t.*,
             row_number() over (order by a) as seqnum_a,
             row_number() over (partition by b order by a) as seqnum_ab
      from t
     ) t;

行号的不同是某些类型的“离岛”问题（基本上是您要的问题）的一种解决方案。为什么行之有效的解释有些棘手。我发现，如果有人看到了子查询的结果，他们通常会明白为什么差异标识相邻行。