Question

我不是那么高级的sql用户。您能否回顾一下我的以下查询是否最佳？或者我可以做一些更优化和更具可读性的事情？

      select  Distinct  DT.Station  , DT.Slot , DT.SubSlot, DT.CompID , CL.CompName
            from    (
                        select  Station, Slot, SubSlot, CompID
                        from    DeTrace
                        where   DeviceID = '1151579773'     
                    ) as DT 
            Left outer CList as CL  
                  on  DT.CompID = CL.CompID 
                  where CL.CompName = '9234220'
                  order by CompName

感谢您的帮助。

Answer 1

这样更容易阅读：

 select  Distinct  DT.Station  , DT.Slot , DT.SubSlot, DT.CompID , CL.CompName
            from  DeTrace DT    
            Left outer join CList as CL  
                  on  DT.CompID = CL.CompID 
                  where CL.CompName = '9234220'
                    and DT.DeviceID = '1151579773'
                  order by CompName

优化器应该能够像您一样高效地执行此查询，但您应该检查查询执行计划以确保。

Answer 2

为什么不呢：

SELECT DISTINCT DT.Station  , DT.Slot , DT.SubSlot, DT.CompID , CL.CompName
FROM DeTrace DT
LEFT OUTER JOIN CList CL ON DT.CompID = CL.CompID
                       AND DT.DeviceID = '1151579773'
                       AND CL.CompName = '9234220'
ORDER BY CL.CompName

Answer 3

我认为你不需要子查询。检查以下内容：

select  Distinct  DT.Station  , DT.Slot , DT.SubSlot, DT.CompID , CL.CompName            
from    DeTrace as DT 
Left outer CList as CL  
on  DT.CompID = CL.CompID 
where CL.CompName = '9234220' and DeviceID = '1151579773'     
            order by CompName

Answer 4

我最喜欢这种方式：

SELECT  DISTINCT
        DeTrace.Station,
        DeTrace.Slot,
        DeTrace.SubSlot,
        DeTrace.CompID,
        CL.CompName
    FROM
        DeTrace
    LEFT OUTER JOIN
        CList AS CL ON
            DeTrace.CompID = CL.CompID
    WHERE
        DeviceID = '1151579773' AND
        CL.CompName = '9234220'
    ORDER BY
        CL.CompName

Answer 5

select  Distinct  DT.Station  , DT.Slot , DT.SubSlot, DT.CompID , CL.CompName                  
from    DeTrace DT
Left outer join CList as CL  
          on  DT.CompID = CL.CompID 
where DT.DeviceID = '1151579773' 
and  CL.CompName = '9234220'    
order by CL.CompName

基于Sql Server Cost的优化程序应该能够确定应用条件的最有效顺序。

左外连接查询优化

5 个答案: