針對多對多關係的SQL Server查詢 - 如何查詢？

Question

這是我對上一個問題的更新：Many to many relationship

以前的解決方案工作正常，但現在我想要改善一點結果。我想將所有波長值都放在一行中。

因此，而不是結果如下：

DateTimeID Wavelength SensorID 
11435 1581,665 334 
11435 1515,166 334 
11435 1518,286 335 

我想有一些與此類似：

DateTimeID Wavelength1 Wavelength2 SensorID 
11435 1581,665 1515,166  334 
11435 1518,286     335 

Answer 1

你可以使用它適用一個row_number()的記錄如下：

select DateTimeID, 
    [1] as Wavelength1, 
    [2] as Wavelength2, 
    SensorId 
from 
(
    select [DateTimeID], [Wavelength], [SensorID], 
    row_number() over(partition by DateTimeID, SensorId 
         order by DateTimeID) rn 
    from yourtable 
) src 
pivot 
(
    max(Wavelength) 
    for rn in ([1], [2]) 
) piv 

參見SQL Fiddle with Demo。

如果你將有數目不詳的wavelength值，那麼你可以使用動態SQL生成這個：

DECLARE @cols AS NVARCHAR(MAX), 
    @query AS NVARCHAR(MAX) 

select @cols = STUFF((SELECT distinct ',' + QUOTENAME('Wavelength'+cast(rn as varchar(50))) 
        from 
        (
         select row_number() over(partition by DateTimeID, SensorId 
               order by DateTimeID) rn 
         from yourtable 
        ) src 
      FOR XML PATH(''), TYPE 
      ).value('.', 'NVARCHAR(MAX)') 
     ,1,1,'') 

set @query = 'SELECT DateTimeID,' + @cols + ', SensorId from 
      (
       select [DateTimeID], [Wavelength], [SensorID], 
        ''Wavelength''+cast(row_number() over(partition by DateTimeID, SensorId 
             order by DateTimeID) as varchar(50)) rn 
       from yourtable 
      ) x 
      pivot 
      (
       max(Wavelength) 
       for rn in (' + @cols + ') 
      ) p ' 

execute(@query) 

見SQL Fiddle with Demo