Question

我有两张桌子：

       A
---------------
No.    Name
1      J.Smith
2      R.Alan
3.     D.Williams


       B
----------------------------
ID.    Date        Address    No.(FK from table A) 
1      10/03/01   blah blah   1
2      08/02/05   blah blah   2
3.     12/01/02   blah blah   3
4.     03/07/11   blah blah   1
5.     30/03/09   blah blah   2

我想连接这两个表，一起根据表B中最近的日期省略具有重复名称的行。例如，如果我使用左内连接将表A和B连接在一起，我将为J获得两行史密斯（基于表B中的第1行和第4行）。我想排除那个日期较旧的日期（表B中的第1行）。

我该怎么做？

编辑：

我需要包含表B中的所有列。

Answer 1

也许是这样的：

;WITH CTE
AS
(
    SELECT
        ROW_NUMBER() OVER(PARTITION BY tblB.[No] ORDER BY tblB.[Date]) AS RowNbr,
        tblB.*
    FROM
        B AS tblB
)
SELECT
    *
FROM
    A AS tblA
    LEFT JOIN CTE
        ON tblA.No=CTE.No
        AND CTE.RowNbr=1

Answer 2

WITH [max_dates] AS (
    SELECT [No], MAX([Date]) AS [Date]
    FROM [TableB]
    GROUP BY [No]
)
SELECT [a].[Name], [b].[Date]
FROM [TableA] AS [a]
JOIN [max_dates] AS [b] ON ([a].[No] = [b].[No])
ORDER BY [a].[No] ASC

Answer 3

SELECT A.No 
     , A.Name
     , C.Date
     , C.Address
     , C. ...
FROM A 
LEFT JOIN
    ( SELECT Address , ... , No, Date,  ROW_NUMBER() OVER(PARTITION BY No ORDER BY Date DESC) AS row
        FROM B 
    ) C ON A.No = C.No 
WHERE C.row = 1

WHERE COALESCE(C.row, 1) = 1 [if there is no link ,and you'll get Date NULL]

编辑：如果B中有很多列

SELECT A.No 
     , A.Name
     , C.* (also row)
FROM A 
LEFT JOIN
    ( SELECT * ,  ROW_NUMBER() OVER(PARTITION BY No ORDER BY Date DESC) AS row
        FROM B 
    ) C ON A.No = C.No 
WHERE C.row = 1

Answer 4

很好地使用了Rory Hunter的CTE，或者没有它：

 SELECT [A].Name, [B].Date
 FROM [A]
     INNER JOIN [B]
         INNER JOIN
         ( -- build a limitation on B
             SELECT No, MaxDate = Max(Date)
             FROM [B]
             GROUP BY No
         ) BLimit
            ON BLimit.No = B.No
            AND BLimit.MaxDate = B.Date
         ON B.No = A.No

BLimit仅限每个No（FK）允许最高日期通过限制器。并且B中的所有字段都可以用于查询，因为限制仅在B上使用BLimit。

SQL Server - 根据最近的日期加入两个表

4 个答案: