出發日期大於抵達日期

Question

如何確保我的出發日期大於下列代碼中的到達日期。

SELECT ArrivalDate, DATEADD(day, RAND(checksum(NEWID()))*1.5 
* LengthOfStay.LengthofStay, ArrivalDate) AS DepartureDate  
FROM Bookings, LengthOfStay 
ORDER BY ArrivalDate 

感謝

韋恩

Answer 1

嘗試此查詢

SELECT * FROM 
    (
     SELECT 
      ArrivalDate, 
      DATEADD(day, RAND(checksum(NEWID()))*1.5 * LengthOfStay.LengthofStay, ArrivalDate) AS DepartureDate  
     FROM 
      Bookings, LengthOfStay 
    ) a 
WHERE a.DepartureDate > a.ArrivalDate 
ORDER BY a.ArrivalDate 

Answer 2

DATEADD取整數...任何十進制值返回從隨機將只被截斷。因此，您可能只需將0添加到ArrivalDate，結果兩個日期相等。

你可以僅僅通過增加最少的1您隨機解決這個問題：

SELECT ArrivalDate, DATEADD(day, 1 + RAND(checksum(NEWID()))*1.5 
* LengthOfStay.LengthofStay, ArrivalDate) AS DepartureDate  
FROM Bookings, LengthOfStay 
ORDER BY ArrivalDate