Question

我一直在练习查询，而我目前的情况是在给定日期找到最近的星期六。在我得到逻辑后，我想出了一个，什么看起来像一个冗长而凌乱的查询。我想知道是否有办法简化这一点。这是我的查询

DECLARE @DATE DATE
SET @DATE ='2013-09-13'

IF              DATENAME(DW,@DATE) = 'SUNDAY'
    BEGIN 
        SELECT  DATEADD(DAY,-1,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'MONDAY'
    BEGIN 
        SELECT  DATEADD(DAY,-2,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'TUESDAY'
    BEGIN 
        SELECT  DATEADD(DAY,-3,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'WEDNESDAY'
    BEGIN 
        SELECT  DATEADD(DAY,3,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'THURSDAY'
    BEGIN 
        SELECT  DATEADD(DAY,2,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'FRIDAY'
    BEGIN 
        SELECT  DATEADD(DAY,1,@DATE) AS DATE, 'IS THE NEAREST SATURDAY'
    END
ELSE IF         DATENAME(DW,@DATE) = 'SATURDAY'
    BEGIN
        SELECT  CONVERT(NVARCHAR,@DATE) + ' IS SATURDAY' AS DATE_DOW
    END

我们可以看到查询很长并且运行多个IF来查找TRUE条件。请不要写查询，只是提示。我想自己处理查询。

Answer 1

这是我的提示，没有回答，正如你所要求的那样：

考虑日期操作，使用当前日期（您可以使用GETDATE()或您的日期变量），DATEADD()和DATEDIFF()可以用来写几行。

如果您只想简化方法，可以使用CASE语句：

DECLARE @date DATE = '2013-09-13'
SELECT CASE WHEN DATENAME(DW,@DATE) = 'SUNDAY' THEN  CAST(DATEADD(DAY,-3,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'MONDAY' THEN CAST(DATEADD(DAY,-2,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'TUESDAY' THEN CAST(DATEADD(DAY,-1,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'WEDNESDAY' THEN CAST(DATEADD(DAY,1,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'THURSDAY' THEN CAST(DATEADD(DAY,2,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            WHEN DATENAME(DW,@DATE) = 'FRIDAY' THEN CAST(DATEADD(DAY,3,@DATE) AS VARCHAR(12)) + ' IS THE NEAREST SATURDAY'
            ELSE CONVERT(NVARCHAR,@DATE) + ' IS SATURDAY'
       END

为了澄清我所暗示的方法并且Sparky发布了，你需要调整DATEFIRST才能使这个工作，它适用于每周的第一天，周六是第7天的一周，所以：

SET DATEFIRST 7
DECLARE @date DATE = '2013-09-21'
SELECT DATEADD(day,7-DATEPART(weekday,@date),@date)

Answer 2

试试这个：

select dateAdd(dd,7-DATEPART(dw,getDate()),GETDATE())

datePart（dw，...）会返回当前日期的星期几。

7 - 该数字，返回星期六的天数

将结果添加到日期以获得下一个星期六...

如果你需要回到上一个星期六那么类似的逻辑

Sql Fiddle：http://www.sqlfiddle.com/#!3/61998/2

Answer 3

不完全是答案，而是另类

    DECLARE @DATE DATE,
    @SUN DATE,
    @MON DATE,
    @TUE DATE,
    @WED DATE,
    @THU DATE,
    @FRI DATE,
    @SAT DATE

           SET @DATE = '2013-09-14'

    SET @SUN = DATEADD(DAY,-1,@DATE)
    SET @MON = DATEADD(DAY,-1,@DATE)
    SET @TUE = DATEADD(DAY,-2,@DATE)
    SET @WED = DATEADD(DAY,-3,@DATE)
    SET @THU = DATEADD(DAY,2,@DATE)
    SET @FRI = DATEADD(DAY,1,@DATE)
    SET @SAT = DATEADD(DAY,0,@DATE)

    SELECT CASE 
        WHEN DATENAME(DW,@DATE) = 'SUNDAY'
        THEN @SUN
        WHEN DATENAME(DW,@DATE) = 'MONDAY'
        THEN @MON
        WHEN DATENAME(DW,@DATE) = 'TUESDAY'
        THEN @TUE
        WHEN DATENAME(DW,@DATE) = 'WEDNESDAY'
        THEN @WED
        WHEN DATENAME(DW,@DATE) = 'THURSDAY'
        THEN @THU
        WHEN DATENAME(DW,@DATE) = 'FRIDAY'
        THEN @FRI
        ELSE @SAT
    END

如何找到给定日期的最近（星期几）

3 个答案: