加入2個表，其中對另一個表

Question

我想加入2個表，但表只有B選擇值其中id是最大的和2列的表之間的匹配選擇最高值A & B.

我都試過，但由於表2的最高值，它只選擇1行，但我需要顯示整個表A.下面

WITH CTE AS 
(
    SELECT DocNum, Status 
    FROM TableB 
    WHERE Id = (SELECT MAX(Id) FROM TableB) 
) 
SELECT TableA.DocNum, DocTitle, cte.Status 
FROM TableA 
INNER JOIN cte 
ON TableA.DocNum = cte.DocNum 

例如：

Table A 
    Id DocNum DocTitle 
    1 ST-0001 SomeTitle 
    2 ST-0002 SomeTitle 
    3 ST-0003 SomeTitle 
    4 ST-0004 SomeTitle 
    5 ST-0005 SomeTitle 

Table B 
    Id DocNum Status 
    1 ST-0001 Incomplete 
    2 ST-0001 Complete 
    3 ST-0002 Complete 
    4 ST-0003 Incomplete 
    5 ST-0004 Incomplete 
    6 ST-0004 Complete 
    7 ST-0005 Incomplete 

Result 
    DocNum DocTitle Status 
    ST-0001 SomeTitle Complete 
    ST-0002 SomeTitle Complete 
    ST-0003 SomeTitle Incomplete 
    ST-0004 SomeTitle Complete 
    ST-0005 SomeTitle Incomplete 

Answer 1

您可以使用CTE與ROW_NUMBER每docNum最大的ID從tableB的只得到了行，然後再加入到該CTE。

首先，創建並填充示例表（請保存我們這一步在你未來的問題）：

DECLARE @A As Table 
(
    Id int, 
    DocNum char(7), 
    DocTitle varchar(20) 
); 

DECLARE @B As Table 
(
    Id int, 
    DocNum char(7), 
    [Status] varchar(20) 
); 

INSERT INTO @A VALUES 
(1, 'ST-0001', 'SomeTitle'), 
(2, 'ST-0002', 'SomeTitle'), 
(3, 'ST-0003', 'SomeTitle'), 
(4, 'ST-0004', 'SomeTitle'), 
(5, 'ST-0005', 'SomeTitle'); 

INSERT INTO @B VALUES 
(1, 'ST-0001', 'Incomplete'), 
(2, 'ST-0001', 'Complete'), 
(3, 'ST-0002', 'Complete'), 
(4, 'ST-0003', 'Incomplete'), 
(5, 'ST-0004', 'Incomplete'), 
(6, 'ST-0004', 'Complete'), 
(7, 'ST-0005', 'Incomplete'); 

然後，創建CTE與tableB的的ROW_NUMBER：

;WITH CTE AS 
(
    SELECT Id, 
      DocNum, 
      [Status], 
      ROW_NUMBER() OVER(PARTITION BY DocNum ORDER BY Id DESC) As Rn 
    FROM @B 
) 

查詢：

SELECT A.DocNum, A.DocTitle, CTE.[Status] 
FROM @A A 
INNER JOIN CTE ON A.DocNum = CTE.DocNum 
WHERE CTE.rn = 1 

結果：

DocNum  DocTitle Status 
ST-0001  SomeTitle Complete 
ST-0002  SomeTitle Complete 
ST-0003  SomeTitle Incomplete 
ST-0004  SomeTitle Complete 
ST-0005  SomeTitle Incomplete 

You can see a live demo on rextester.