2

我需要在进行 GROUP BY 时找出值来自的行 ID。

首先创建并填充一个“播放对象”

-- vertical coalesce with row-source of value :) instead of column-source of value as in horizontal coalesce :)
CREATE TABLE #TBL(ID INT, GR INT, A INT, B INT)
INSERT INTO #TBL
SELECT 1,1,1,NULL
UNION ALL SELECT 2,1,NULL,2
UNION ALL SELECT 3,1,NULL,3
UNION ALL SELECT 4,2,2,NULL
UNION ALL SELECT 5,2,NULL,NULL
UNION ALL SELECT 6,2,6,NULL

选择最小值很简单：

SELECT GR, MIN(A) A, MIN(B) B,
    'Which first available row did A come from?' A_ID, 
    'Which first available row did B come from?' B_ID 
FROM #TBL
GROUP BY GR

但回答问题不是！

我试图做子查询，但由于值来自不同的行，它不起作用：

SELECT a.*
from #TBL a
    join (
    SELECT GR, MIN(A) A, MIN(B) B,
        'Which row did A come from?' A_ID, 
        'Which row did B come from?' B_ID
    FROM #TBL
    GROUP BY GR) b on a.GR = b.GR and a.A = b.A and a.B = b.B
--DROP TABLE #TBL

请帮忙。

4

3 回答 3

2

我不确定它是否会执行连接/外部应用（我认为它会），但这会起作用：

WITH CTE AS
(   SELECT  GR, 
            A, 
            B, 
            ID, 
            MinA = MIN(A) OVER(PARTITION BY GR), 
            MinB = MIN(B) OVER(PARTITION BY GR)
    FROM    #TBL
)
SELECT  GR,
        A = MIN(A),
        B = MIN(B),
        A_ID = MIN(CASE WHEN MinA = A THEN ID END),
        B_ID = MIN(CASE WHEN MinB = B THEN ID END)
FROM    CTE
GROUP BY GR;

在这个小样本上，统计数据表明这个表现更好：

使用聚合

（估计）查询成本 13%

表“工作台”。扫描计数 3，逻辑读取 21，物理读取 0，预读读取 0，lob 逻辑读取 0，lob 物理读取 0，lob 预读读取 0。

使用外部应用

（估计）查询成本 87%

表“工作台”。扫描计数 16，逻辑读取 42，物理读取 0，预读读取 0，lob 逻辑读取 0，lob 物理读取 0，lob 预读读取 0。

但是您可能会发现带有索引的实际示例会有所不同。

于 2013-09-26T16:23:56.870 回答
1

这应该这样做：

SELECT  DISTINCT 
        T1.GR,
        T2.A,
        T3.B,
        T2.ID A_ID,
        T3.ID B_ID
FROM #TBL T1
OUTER APPLY (SELECT TOP 1 *
             FROM #TBL
             WHERE GR = T1.GR
             AND A IS NOT NULL
             ORDER BY A, ID) T2
OUTER APPLY (SELECT TOP 1 *
             FROM #TBL
             WHERE GR = T1.GR
             AND B IS NOT NULL
             ORDER BY B, ID) T3

结果：

╔════╦═══╦══════╦══════╦══════╗
║ GR ║ A ║  B   ║ A_ID ║ B_ID ║
╠════╬═══╬══════╬══════╬══════╣
║  1 ║ 1 ║ 2    ║    1 ║ 2    ║
║  2 ║ 2 ║ NULL ║    4 ║ NULL ║
╚════╩═══╩══════╩══════╩══════╝
于 2013-09-26T16:19:30.540 回答
0 
;WITH CTEA AS
(   SELECT  ID, GR, A, ROW_NUMBER() OVER(PARTITION BY GR ORDER BY A) AS 'RowNum'
    FROM    #TBL where A is not null
),    CTEB AS
(   SELECT  ID, GR, B, ROW_NUMBER() OVER(PARTITION BY GR ORDER BY B) AS 'RowNum'
    FROM    #TBL where B  is not null
)
select  CTEA.GR, CTEA.A, CTEA.ID, CTEB.B, CTEB.ID
  from  CTEA 
  jull  outer join  CTEB
    on  CTEA.GR = CTEB.GR
   and  CTEA.RowNum = 1 
   and  CTEB.RowNum = 1
于 2013-09-26T17:13:52.547 回答