sql - 只选择第一个结果...有更好的方法吗？

Question

可以有多个 Config_RecID，但我只想显示附加到 SR_Service_RecID 的第一个，或者当为 null 时显示 NULL。

SELECT s.SR_Service_RecID
     , sc.Config_RecID

  FROM SR_Service s
       LEFT JOIN SR_Config sc
              ON sc.SR_Service_RecID = s.SR_Service_RecID

 WHERE (sc.Config_RecID = 
       (
           SELECT TOP 1 sc.Config_RecID
             FROM SR_Config sc 
            WHERE sc.SR_Service_RecID = s.SR_Service_RecID
       ) 
       OR sc.Config_RecID IS NULL)

有更好/更简洁的方法来做到这一点，还是我走在正确的道路上？

Answer 1

您可以将条件移至 ON 子句中:

SELECT s.SR_Service_RecID
     , sc.Config_RecID
FROM SR_Service s
LEFT JOIN SR_Config sc
     ON sc.SR_Service_RecID = s.SR_Service_RecID
     AND sc.Config_RecID = (
           SELECT TOP 1 Config_RecID
           FROM SR_Config sc2 
           WHERE sc2.SR_Service_RecID = s.SR_Service_RecID
     )

这样您就不需要额外检查 sc.Config_RecID IS NULL