多列的最大日期？

Question

如何在多列的最大值中每行返回 1 个值：

TableName [RefNumber, FirstVisitedDate, SecondVisitedDate, RecoveryDate, ActionDate]

我希望 MaxDate of (FirstVisitedDate, SecondVisitedDate, RecoveryDate, ActionDate) 这些日期用于单列中的所有行，并且我想要另一个新列 (Acion) 取决于 Max date 列，例如：如果 Max date 来自 FirstVisitedDate 那么它将是“FirstVisited”，或者如果 Max 日期来自 SecondVisitedDate，那么它将是“SecondVisited”...

总的结果喜欢：

从表中选择 RefNumber、Maxdate、Action 按 RefNumber 分组

Answer 1

四列的蛮力方法还不错：

select (case when FirstVisitedDate >= SecondVisitedDate and
                  FirstVisitedDate >= RecoveryDate and
                  FirstVisitedDate >= ActionDate
             then FirstVisitedDate
             when SecondVisitedDate >= RecoveryDate and
                  SecondVisitedDate >= ActionDate
             then SecondVisitedDate 
             when RecoveryDate >= ActionDate
             then RecoveryDate
             else ActionDate
        end),
       (case when FirstVisitedDate >= SecondVisitedDate and
                  FirstVisitedDate >= RecoveryDate and
                  FirstVisitedDate >= ActionDate
             then 'FirstVisitedDate'
             when SecondVisitedDate >= RecoveryDate and
                  SecondVisitedDate >= ActionDate
             then 'SecondVisitedDate'
             when RecoveryDate >= ActionDate
             then 'RecoveryDate'
             else 'ActionDate'
        end)     
from table t;

编辑：

在group by 中这样做只是添加聚合函数的问题：

select RefNumber,
       (case when max(FirstVisitedDate) >= max(SecondVisitedDate) and
                  max(FirstVisitedDate) >= max(RecoveryDate) and
                  max(FirstVisitedDate) >= max(ActionDate)
             then max(FirstVisitedDate
             when max(SecondVisitedDate) >= max(RecoveryDate) and
                  max(SecondVisitedDate) >= max(ActionDate)
             then max(SecondVisitedDate) 
             when max(RecoveryDate) >= max(ActionDate)
             then max(RecoveryDate)
             else max(ActionDate)
        end),
       (case when max(FirstVisitedDate) >= max(SecondVisitedDate) and
                  max(FirstVisitedDate) >= max(RecoveryDate) and
                  max(FirstVisitedDate) >= max(ActionDate)
             then 'FirstVisitedDate'
             when max(SecondVisitedDate) >= max(RecoveryDate) and
                  max(SecondVisitedDate) >= max(ActionDate)
             then 'SecondVisitedDate'
             when max(RecoveryDate) >= max(ActionDate)
             then 'RecoveryDate'
             else 'ActionDate'
        end)     
from table t
group by RefNumber;

Answer 2

;WITH cte AS (
  -- Build table of date 
  SELECT [RefNumber], 
         [ActionDate]= [FirstVisitedDate], 
         [Action] = 'First Visited' 
  FROM [Table1] 
  UNION ALL
  SELECT [RefNumber], 
         [SecondVisitedDate],  
         'Second Visited' 
  FROM [Table1] 
  UNION ALL
  SELECT [RefNumber], 
         [RecoveryDate], 
         'Recover'
  FROM [Table1]
), cte2 AS (
  -- Add row_number to pull most recent to top
  SELECT  [RefNumber],
          [Action],
          [ActionDate],
          [DateRank] = 
              ROW_NUMBER() OVER (PARTITION BY RefNumber 
                                 ORDER BY [ActionDate] DESC)
  FROM [cte]
)
-- select only the most recent
SELECT * 
FROM cte2 
WHERE [DateRank] = 1

Answer 3

SELECT RecordID, MaxDate
FROM SourceTable
    CROSS APPLY (SELECT MAX(d) MaxDate 
                FROM (VALUES (date1), (date2), (date3), 
                             (date4), (date5), (date6), 
                             (date7)) AS dates(d)) md

Answer 4

我为此编写了一个自定义函数：

CREATE FUNCTION [dbo].[MaxOf5]
(
    @D1 DateTime,
    @D2 DateTime,
    @D3 DateTime,
    @D4 DateTime,
    @D5 DateTime
)
RETURNS DateTime
AS
BEGIN
    DECLARE @Result DateTime

    SET @Result = COALESCE(@D1, @D2, @D3, @D4, @D5)

    IF @D2 IS NOT NULL AND @D2 > @Result SET @Result = @D2
    IF @D3 IS NOT NULL AND @D3 > @Result SET @Result = @D3
    IF @D4 IS NOT NULL AND @D4 > @Result SET @Result = @D4
    IF @D5 IS NOT NULL AND @D5 > @Result SET @Result = @D5

    RETURN @Result
END

要调用它并计算您的 Action 列，这应该可以工作：

SELECT
    MaxDate,
    CASE WHEN MaxDate = FirstVisitedDate THEN 'FirstVisited'
       WHEN MaxDate = SecondVisitedDate THEN 'SecondVisited'
       WHEN MaxDate = RecoveryDate THEN 'Recovery'
       WHEN MaxDate = ActionDate THEN 'Action'
    END AS [Action]
FROM (
    SELECT
       RefNumber,
       dbo.MaxOf5(FirstVisitedDate, SecondVisitedDate, RecoveryDate, ActionDate) AS MaxDate,
       FirstVisitedDate, SecondVisitedDate, RecoveryDate, ActionDate
    FROM table
) AS data

请注意，您可以将多个日期与最大日期绑定。在这种情况下，WHEN 子句的顺序决定了哪一个获胜。