移動X天的T-SQL數據時間列重疊UNIQUE約束

Question

問題是在具有唯一值約束的列上使用DATEADD函數，同時考慮到新值將與現有值重疊並且實際上會存在違反約束的事實，因爲我們不能有兩個具有相同日期的行。

例如我有表[SomeDate]是DateTime類型的表，並且約束是唯一的。我的日期從2017-01-01開始到2018-01-01爲止，並且希望通過爲每個人添加7天來更新記錄。

Answer 1

其中一種可能的方法是將未來日期移出當前的最小 - 最大範圍，然後再考慮我們要添加的天數。這裏是準備好和工作的解決方案：

--Number of days we want to add to existing dates 
DECLARE @daysToMoveAhead int = 7; 

DECLARE @minDate datetime = (SELECT MIN([SomeDate]) from dbo.MyTable) 
DECLARE @maxDate datetime = (SELECT MAX([SomeDate]) from dbo.MyTable) 

DECLARE @diff int = DATEDIFF(DAY,@minDate,@maxDate) 

--temporary move the dates out of existing min-max range 
update dbo.MyTable set [SomeDate] = DATEADD(DAY, @diff,[SomeDate]); 

--bring dates back and add as many days as we wanted 
update dbo.MyTable set [SomeDate] = DATEADD(DAY, @daysToMoveAhead - @diff,[SomeDate]); 

Answer 2

如果您更新所有行，那麼唯一約束應該沒有問題。
下面是一個簡單的例子：

CREATE TABLE T 
(
    SomeDate date NOT NULL, 
    CONSTRAINT uc UNIQUE (SomeDate) 
) 

;WITH CTE AS 
(
    SELECT CAST(GETDATE() As Date) As TheDate 
    UNION ALL 
    SELECT CAST(DateADD(DAY, 1, TheDate) As Date) 
    FROM CTE 
    WHERE TheDate < DATEADD(DAY, 10, GETDATE()) 
) 

INSERT INTO T(SomeDate) 
SELECT TheDate 
FROM CTE 

UPDATE T 
SET SomeDate = DATEADD(DAY, 3, SomeDate) 

You can see it in action on rextester