SQL Server查询多对多关系

在大多数情况下,表tblWavelengths中有2行与表tblSensors相关,(在某些情况下只有1行,在极端情况下可能有20行)

我做了以下简单查询来从这3个表中检索数据：

select W.DateTimeID,S.SensorName,S.SensorType,W.Channel,W.PeakNr,W.Wavelength
from tblWavelengths as W
    Left Join tblSensorWavelengths as SW on W.tblWavelengthID = SW.WavelengthID
    Left Join tblSensors as S on SW.SensorID = S.SensorID
order by W.DateTimeID

运行此查询后,我得到以下结果：

这是我的问题.我想写一个查询,它只过滤那些传感器(SensorName),它在给定的时刻(DateTimeID)在tblWavelengths表中有两行(两个不同的波长).所以例如我想要没有结果
77902/001传感器 – 因为它在给定时刻只有一行(一个波长)与tblSensors相关

解决方法

WITH Data AS
(   SELECT  W.DateTimeID,W.Wavelength,[Wcount] = COUNT(*) OVER(PARTITION BY s.SensorName,d.DateTimeID)
    from    tblWavelengths as W
            LEFT JOIN tblSensorWavelengths as SW 
                ON W.tblWavelengthID = SW.WavelengthID
            LEFT JOIN tblSensors as S 
                ON SW.SensorID = S.SensorID
)
SELECT  DateTimeID,SensorName,SensorType,Channel,PeakNr,WaveLength
FROM    Data
WHERE   Wcount = 2
ORDER BY DateTimeID;

附录

后来我意识到你可能有两个结果,同时一个传感器具有相同的波长,这将返回2个记录,但没有两个不同的波长.由于窗口函数不支持使用DISTINCT,因此下面是另一种选择

WITH Data AS
(   SELECT  W.DateTimeID,W.tblWaveLengthID
    from    tblWavelengths as W
            LEFT JOIN tblSensorWavelengths as SW 
                ON W.tblWavelengthID = SW.WavelengthID
            LEFT JOIN tblSensors as S 
                ON SW.SensorID = S.SensorID

)
SELECT  d.DateTimeID,d.SensorName,d.SensorType,d.Channel,d.PeakNr,d.WaveLength
FROM    Data d
        INNER JOIN
        (   SELECT  DateTimeID,SensorName
            FROM    Data
            GROUP BY DateTimeID,SensorName
            HAVING  COUNT(DISTINCT tblWaveLengthID) = 2
        ) t
            ON t.DateTimeID = d.DateTimeID
            AND t.SensorName = d.SensorName
ORDER BY d.DateTimeID;

（编辑：李大同）

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