在函數中計算日期

Question

1  28/11/2011 ... 

如何在SQL中編寫函數來實現上述模式？

Answer 1

你可以做在SQL Server中是這樣的：

DECLARE @BaseDate DATE = '20111107'; 
DECLARE @EndDate DATE = GETDATE(); --Or the "end of dates in the database" 
WITH RecursiveCTE AS (
    SELECT 
     1 AS [Counter], 
     @BaseDate AS [MyDate] 
    UNION ALL 
    SELECT 
     [Counter] + 1, 
     DATEADD(DAY, 7, MyDate) 
    FROM 
     RecursiveCTE 
    WHERE 
     MyDate < @EndDate) 
SELECT * FROM RecursiveCTE OPTION (MAXRECURSION 0); 

處理日期未準確，使這成爲一個功能，你可以這樣做：

--Function definition 
CREATE FUNCTION SuperDuperDataCalculator (
    @BaseDate DATE = '20131016', 
    @EndDate DATE = '20131020') 
RETURNS @Results TABLE (
    [Counter] INT, 
    [Date] DATE) 
AS 
BEGIN 
    WITH RecursiveCTE AS (
     SELECT 
      1 AS [Counter], 
      @BaseDate AS [MyDate] 
     UNION ALL 
     SELECT 
      [Counter] + 1, 
      CASE WHEN DATEADD(DAY, 7, MyDate) > @EndDate THEN @EndDate ELSE DATEADD(DAY, 7, MyDate) END 
     FROM 
      RecursiveCTE 
     WHERE 
      MyDate < @EndDate) 
    INSERT INTO 
     @Results 
    SELECT * FROM RecursiveCTE OPTION (MAXRECURSION 0); 
    RETURN; 
END; 
GO 

--Usage 
SELECT * FROM SuperDuperDataCalculator('20131016', '20131020'); 

--Results 
Counter Date 
1 2013-10-16 
2 2013-10-20 

請注意，我們必須使用多語句表值函數，因爲在SQL Server中的錯誤，它不會讓你用一個簡單的表值函數的選擇。另一種方法是從函數中刪除OPTION（MAXRECURSION 0），並記住在每次引用它時使用它（即相當差的選擇）。

...最後，如果你想只返回計數器值的最大值，你可以重寫這是一個標量值函數，即：

--Function definition 
CREATE FUNCTION SuperDuperDataCalculator (
    @BaseDate DATE = '20131016', 
    @EndDate DATE = '20131020') 
RETURNS INT 
AS 
BEGIN 
    DECLARE @Results TABLE (
    [Counter] INT, 
    [Date] DATE); 
    DECLARE @ReturnValue INT; 
    WITH RecursiveCTE AS (
     SELECT 
      1 AS [Counter], 
      @BaseDate AS [MyDate] 
     UNION ALL 
     SELECT 
      [Counter] + 1, 
      CASE WHEN DATEADD(DAY, 7, MyDate) > @EndDate THEN @EndDate ELSE DATEADD(DAY, 7, MyDate) END 
     FROM 
      RecursiveCTE 
     WHERE 
      MyDate < @EndDate) 
    INSERT INTO 
     @Results 
    SELECT * FROM RecursiveCTE OPTION (MAXRECURSION 0); 
    SELECT @ReturnValue = MAX([Counter]) FROM @Results; 
    RETURN @ReturnValue; 
END; 
GO 
SELECT dbo.SuperDuperDataCalculator('20131016', '20131020'); 

Answer 2

試試這個 - 這將讓所有的周在子查詢中分配一個rownumber。然後只選擇行號= 1的記錄，因爲該周可能會有更多結果。所以因此RowNo = 1

SELECT ROW_NUMBER() OVER(ORDER BY RowNo) AS IncrementalWeek,dte 
FROM 
(
     SELECT DISTINCT DATEPART(ww,CONVERT(VARCHAR(20),createdDate,111)) AS [week], 
         CONVERT(VARCHAR(20),createdDate,111) AS dte, 
         ROW_NUMBER() OVER(PARTITION BY DATEPART(ww,Convert(VARCHAR(20),createdDate,111)) ORDER BY DATEPART(ww,CONVERT(VARCHAR(20),createdDate,111))) AS RowNo 
     FROM YourTable 

) AS tble 
WHERE RowNo = 1 
ORDER BY [week]