Left outer Join query optimization

Question

I am not so advanced sql user. Could you please review my following query is it optimal ? or I can do something more more optimized and more readable?

      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 

Thanks for help.

Answer 1

It is easier to read like this:

 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 

The optimiser should be able to perform this query as efficiently as yours, but you should check the query execution plan just to be sure.

Answer 2

Why not just:

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

I think you don't need subquery. Check below:

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

I like this way best:

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

The Sql Server Cost Based Optimizer should be able to determine the most efficient order in which to apply the conditions.