查找SQL Server中当前年份日期给出的上一年的同一天

Question

我正在使用SQL Server,该方案是查找截至今天的同一天的上一年的日期.

假设2014-03-06是今天日期和星期四是星期四我想在同一周找到前一个谎言的同一天.这是2013-03-07

任何身体可以帮助吗？这是我写的:

 DECLARE @DateFrom AS DATETIME
 DECLARE @DateTo AS DATETIME 


SET @DateFrom = '2014-01-01'
SET @DateTo = '2014-02-10'


DECLARE @Count AS INT

SET @Count = DATEDIFF(DAY, @DateFrom, @DateTo)


CREATE TABLE #current_year /*This Year*/
(
  [Date] DATETIME ,
  WeekNum INT,
  [Day] VARCHAR(20),
  Data INT
)
CREATE TABLE #last_year /*This Year -1*/
(
  [Date] DATETIME ,
  WeekNum INT,
  [Day] VARCHAR(20),
  Data INT
)
WHILE ( @Count > 0 ) 
        BEGIN
            INSERT  INTO #current_year
            VALUES  ( CONVERT(VARCHAR(10), @DateFrom, 101),                        
                      DATEPART(week,@DateFrom),
                      DATENAME(weekday, @DateFrom),@Count)          
            INSERT  INTO #last_year
            VALUES  ( CONVERT(VARCHAR(10), DATEADD(YEAR, -1, @DateFrom), 101),                                                  
                      DATEPART(week,DATEADD(YEAR,1,@DateFrom)),
                      DATENAME(weekday, DATEADD(YEAR, -1, @DateFrom)),@Count)  
            SET @DateFrom = DATEADD(day, 1, @DateFrom)
            SET @Count = @Count - 1
        END      
        SELECT * from #current_year     
        SELECT * from #last_year   

        SELECT CONVERT(varchar(10),#current_year.[Date],111) AS CYDate,
               --ISNULL(CONVERT(varchar(10),#last_year.[Date],111) ,/*CONVERT(varchar(10),DateAdd(dd, 1, DATEADD(yy, -1, #current_year.Date)),111)*/) AS LYDate
               --CONVERT(varchar(10),#last_year.[Date],111) AS LYDate
               Coalesce(CONVERT(varchar(10),#last_year.[Date],111) ,DateAdd(dd, 1, DATEADD(yy, -1, #current_year.Date))) AS LYDate,
               #current_year.Data AS CD,
               #last_year.Data AS LD
               FROM #current_year                            
               --LEFT JOIN #last_year ON #last_year.WeekNum = #current_year.WeekNum
   --                                 AND #last_year.[Day] = #current_year.[Day]
                                    Left JOIN #last_year ON #last_year.WeekNum =  DatePart(wk, GETDATE())



DROP TABLE #current_year
DROP TABLE #last_year

这是输出:

这是添加解决方案后的输出,现在在左连接中它排除了前一年的(NULL)数据

Answer 1

基本上你需要找到这个和前几年相同日期之间的天数差异,然后通过mod 7理解"天差",并将其与上一年的日期相加:

DECLARE @now DATETIME
SET @now = '2014-03-06'


SELECT CAST (DATEADD(YEAR, -1, @now) + (CAST (@now as INT) - CAST (DATEADD(YEAR, -1, @now) AS INT)) % 7 AS DATE)

返回

2013-03-07

Answer 2

尝试

DECLARE @now Date
SET @now = '2014-06-03'
SELECT DATEADD(week, -52, @now)