SQL更新以记录最近的数据

UPDATE  Table1
SET     Date2 = t2.Date2
FROM    Table1 t1
JOIN    Table2 t2
    ON  t1.Name = t2.Name
    AND ABS(DATEDIFF(d, t1.Date1, t2.Date2)) = (SELECT  MIN(ABS(DATEDIFF(d, t1.Date1, t2.Date2)))
                                                FROM    Table1 t1
                                                JOIN    Table2 t2
                                                    ON  t1.Name = t2.Name
                                                )

检查一下你是否需要 ABS -我想是的。

此外,该查询不处理表2中有两个日期与Date1的距离相同,但来自不同侧面的情况。

WITH abcd AS
 (
 SELECT t1.Name,t1.Date1, t2.Date2
  ,RANK() OVER (ORDER BY ABS(DATEDIFF(dd, t1.Date1, t2.Date2)) ASC) AS rnk
 FROM 
  Table1 AS t1 
  JOIN Table2 AS t2 ON t1.Name = t2.Name
 )
UPDATE Table1 SET
    [Date2] = (SELECT TOP(1) [Date2] FROM abcd WHERE rnk = 1)