SQL 服务器 - ROW_NUMBER() -> 再次重置？

Question

我们在当前编写的查询中遇到了一个特定问题。这是示例：

Doc. ID | Timestamp | Employee 
 01     | 01        | A        
 01     | 02        | B        
 01     | 03        | B        
 01     | 04        | C        
 01     | 05        | A        
 01     | 06        | A

我们要实现的是：

Doc. ID | Timestamp | Employee 
 01     | 01        | A        
 01     | 03        | B        
 01     | 04        | C        
 01     | 06        | A

这是我们的方法（没有用）：

SELECT [Doc. ID], [Timestamp], [Employee]
       ,ROW_NUMBER() OVER (PARTITION BY [Doc. ID],[Employee] order by [Employee] desc) as "RN"
FROM XY
WHERE "RN" = 1

但不幸的是这不起作用，因为在底部再次找到 A 时 Row_number 不会重置。它得到的结果（没有 where 子句）是：

 Doc. ID | Timestamp | Employee | RN
  01     | 01        | A        | 1
  01     | 02        | B        | 1
  01     | 03        | B        | 2
  01     | 04        | C        | 1
  01     | 05        | A        | 2
  01     | 06        | A        | 3

我认为实现正确的解决方案只是多了一点点.. :)

Answer 1

使用 lead() 在 "next" 行中的员工值达到峰值：

select xy.*
from (select xy.*,
             lead(employee) over (partition by docid order by timestamp) as next_employee
      from xy
     ) xy
where next_employee is null or next_employee <> employee;

Answer 2

我想你想要聚合：

SELECT [doc. ID], MAX([Timestamp]) AS [Timestamp], employee
FROM (SELECT t.*,
             row_number() over (order by [Timestamp]) as seq1,
             row_number() over (partition by [doc. ID], employee order by [Timestamp]) as seq2
      FROM XY t
     ) t
GROUP BY [doc. ID], employee, (seq1 - seq2)
ORDER BY [Timestamp];

SQL 服务器 - ROW_NUMBER() -> 再次重置？

SQL Server - ROW_NUMBER() -> Reset again?

sql

sql-server

window-functions