Trying to sum distinct values SQL

Question

I'm having trouble coming up with a value for a cell in SSRS, which should be a sum of distinct values. I have a SSRS report that looks similar to the below screenshot:

I'm having trouble getting the value in red ($11.25). I basically need to sum the Ship Cost, based on distinct Tracking #s. So there are two distinct tracking #s, one with a Ship Cost of $5.25 and the other $6.00, so the total displayed in red should be $11.25. But I cannot achieve this in SSRS and can't figure it out in the SQL query either.

I'm thinking a subquery like (and I know the below is not valid SQL):

(SELECT SUM([Ship Cost]) WHERE [Tracking #] IS DISTINCT) AS [Ship Cost]

But I don't know how to write it.

Answer 1

Get the distinct list first...

SELECT SUM(SQ.COST)
FROM
(SELECT DISTINCT [Tracking #] as TRACK,[Ship Cost] as COST FROM YourTable) SQ

Answer 2

You can do the following:

SELECT SUM(distinct [Ship Cost]) . . .

But, I don't recommend this. You could have two items with the same cost and only one would be counted.

The better way is to select one value for each Tracking #, using the row_number() function:

select SUM(case when seqnum = 1 then [Ship Cost] end)
from (select t.*,
             row_number() over (partition by [Order #], [Tracking #]
                                order by (select NULL)
                               ) as seqnum
      . . .
     ) t