在单独的列中获取最大日期（月和年）

Question

我有这张桌子：

Month   Year    Provider    Number
1       2015    1           345
2       2015    1           345
3       2015    1           345
12      2015    2           444
1       2016    2           444

假设我想按提供商获取所有不同的数字，但只能获取最大月份和最大年份，如下所示：

Month   Year    Provider    Number
3       2015    1           345
1       2016    2           444

我有一个我想改进的丑陋查询：

SELECT (SELECT max([Month]) 
        FROM dbo.Info b
        WHERE b.Provider = a.Provider
          AND b.Number = a.Number
          AND [Year] = (SELECT max([Year]) 
                          FROM dbo.Info c
                         WHERE c.Provider = a.Provider
                           AND c.Number = a.Number)) AS [Month],
        (SELECT max([Year]) 
           FROM dbo.Info d
          WHERE d.Provider = a.Provider
            AND d.Number = a.Number)) AS [Year],
        a.Provider,
        a.Number
 FROM dbo.Info a

Answer 1

一种选择是使用row_number ：

select *
from (
    select *, row_number() over (partition by provider 
                                 order by [year] desc, [month] desc) rn
    from dbo.Info
) t
where rn = 1

假定数字和提供者字段相同。 如果不是，您可能还需要按数字字段进行分区。

Answer 2

您可以使用row_number和cte

;WITH cte AS (
  SELECT 
    *,
    ROW_NUMBER() OVER (PARTITION BY Provider ORDER BY [Year] DESC, [Month] DESC) as rNum
  FROM Info)

SELECT *
FROM cte where rNum = 1

如果要创建视图，则

CREATE VIEW SomeViewName
AS

WITH cte AS (
  SELECT 
    *,
    ROW_NUMBER() OVER (PARTITION BY Provider ORDER BY [Year] DESC, [Month] DESC) as rNum
  FROM Info)

SELECT *
FROM cte where rNum = 1