從所有列中獲取最後一個NOT NULL值

Question

我有一種情況，我試圖從所有列中獲取最後一個非空值。這裏是一些數據來演示puposes。

測試數據

DECLARE @t TABLE (ID INT, Col1 INT, Col2 INT, Col3 INT, Dated DATETIME) 
INSERT INTO @t VALUES 
(1, NULL, 100 , NULL, '20131210'), --<-- Column2 from this row 
(1, 20 , 200 , NULL, '20131209'), --<-- Column1 from this row 
(1, 30 , NULL , 300 , '20131208'), --<-- Column3 from this row 
(1, 40 , 400 , NULL, '20131207') 

╔════╦══════╦══════╦══════╦═════════════════════════╗ 
║ ID ║ Col1 ║ Col2 ║ Col3 ║   Dated   ║ 
╠════╬══════╬══════╬══════╬═════════════════════════╣ 
║ 1 ║ NULL ║ 100 ║ NULL ║ 2013-12-10 00:00:00.000 ║ 
║ 1 ║ 20 ║ 200 ║ NULL ║ 2013-12-09 00:00:00.000 ║ 
║ 1 ║ 30 ║ NULL ║ 300 ║ 2013-12-08 00:00:00.000 ║ 
║ 1 ║ 40 ║ 400 ║ NULL ║ 2013-12-07 00:00:00.000 ║ 
╚════╩══════╩══════╩══════╩═════════════════════════╝ 

我建立了一個查詢返回所需的結果。但是想知道是否有更高性能的這種做法。由於這種方式，我每次希望找到獲得這些結果的更有效方法時，都在嘲笑整個表格。

我的查詢

SELECT ColumnName, Col1 AS Value, Dated 
FROM 
(
SELECT TOP 1 'Column1' AS ColumnName 
      , Col1 
      , Dated 
FROM @t 
WHERE Col1 IS NOT NULL 
ORDER BY Dated DESC 
)Q1 

UNION ALL 

SELECT * FROM 
(
SELECT TOP 1 'Column2' AS ColumnName 
      , Col2 
      , Dated 
FROM @t 
WHERE Col2 IS NOT NULL 
ORDER BY Dated DESC 
)Q2 

UNION ALL 

SELECT * FROM 
(
SELECT TOP 1 'Column3' AS ColumnName 
      , Col3 
      , Dated 
FROM @t 
WHERE Col3 IS NOT NULL 
ORDER BY Dated DESC 
)Q3 

結果集

╔════════════╦═══════╦═════════════════════════╗ 
║ ColumnName ║ Value ║   Dated   ║ 
╠════════════╬═══════╬═════════════════════════╣ 
║ Column1 ║ 20 ║ 2013-12-09 00:00:00.000 ║ 
║ Column2 ║ 100 ║ 2013-12-10 00:00:00.000 ║ 
║ Column3 ║ 300 ║ 2013-12-08 00:00:00.000 ║ 
╚════════════╩═══════╩═════════════════════════╝ 

它返回正確的結果。但我確信它可以通過更簡單/高效的查詢完成。任何幫助或指針是多少appericiated

Answer 1

差不多一個簡單的UNPIVOT操作和一個合適的ROW_NUMBER來選擇最近的值。該UNPIVOT自動消除NULL值：

;With Numbered as (
    select *,ROW_NUMBER() OVER (PARTITION BY Col ORDER BY Dated desc) rn 
    from @t 
    unpivot (Value for Col in (Col1,Col2,Col3)) p 
) 
select * from Numbered where rn = 1 

結果：

ID   Dated     Value  Col  rn 
----------- ----------------------- ----------- -------- -------------------- 
1   2013-12-09 00:00:00.000 20   Col1  1 
1   2013-12-10 00:00:00.000 100   Col2  1 
1   2013-12-08 00:00:00.000 300   Col3  1 

Answer 2

我認爲，在垂直行格式的UNION選擇是好，但如果你需要它在水平列的格式，那麼你可以使用自加入像下面

SELECT top 1 t1.Col1, t2.Col2, t3.col3 
FROM @t t1 
inner join @t t2 on t2.col2 is not null 
inner join @t t3 on t3.col3 is not null 
where t1.col1 is not null 
order by t1.dated desc