SELECT DISTINCT does not work - Another Problem!

Question

Dear All
Previous Post
I just posted a thread, which has been answered by an expert. It's here:
SELECT DISTINCT does not work. Why?
My original problem was that the Query returned duplicate records, and SELECT DISTINCT did not work.
The solution was to change this select:
T0.[U_SupInv]      AS 'Link'
... to this:
CAST(T0.[U_SupInv] as nvarchar(100))      AS 'Link'
The amended Query worked.
New Problem
I just discovered that resolving the problem created a new one.
The field U_SupInv (Link) is in fact a UDF.
I created it so that all Suppliers' Invoices could be Scanned to pdf files, and these pdf could be linked
to the respective AP Invoice.
Originally, when I clicked 'Link' in my Query results, the pdf scan pops up.
When the Query is amended by adding CAST, the link becomes dead.
Help
Could anyone tell me how I can make SELECT DISTINCT work, as well keeping the LINKS live?
The main purpose of my Query is to help users view the pdf scans by clicking on the links.
Thanks
Leon Lai
Here's my Original Query
SELECT
T0.[UpdateDate] AS 'Update Dt',
T0.[TaxDate] AS 'Doc Dt',
CASE T5.[TransType]
     WHEN '18' THEN 'PU ' + CONVERT(VARCHAR(6), T0.[DocNum])
     WHEN '19' THEN 'PC ' + CONVERT(VARCHAR(6), T0.[DocNum])
END 'SAP Ref.',
T1.[ImportLog]     AS 'Ship #',
T0.[CardCode] + '' AS 'Supplier #',
T0.[CardName]      AS 'Supplier Name',
T0.[DocTotal]      AS 'Rs',
T1.[BlockNum]      AS 'Reqn #',
T0.[DocNum]        AS 'Doc No',
T0.[U_SupInv]      AS 'Link'
FROM klship.[dbo].[OPCH] T0
INNER JOIN klship.[dbo].[PCH1] T1 ON T0.[DocEntry] = T1.[DocEntry]
INNER JOIN klship.[dbo].[OJDT] T5 ON T0.[TransID] = T5.[TransID]
WHERE
(T0.[UpdateDate] >= '[%2]' AND
T0.[UpdateDate]  <= '[%3]' AND
T0.[U_SupInv] IS NULL)
OR
(T0.[UpdateDate] >= '[%4]' AND
T0.[UpdateDate]  <= '[%5]' AND
T0.[U_SupInv] IS NOT NULL)
FOR BROWSE

Answer 1

Dear István Korös,
Thanks a lot for your answer.
I will test your suggestion tomorrow, as it's night and I am returning home now.
However, I do not think it will suit my requirements for the foll reasons:
- I worked hard to get rid of the need to enter anything in the @Scan2 field.
- This UDF was created solely as a text of instruction for my staff.
   Unfortunately I had to fill in something to make the Query work.
- The problem is that if the user forgets to click the drop-down arrow and leaves @Scan2
   blank, the query does not work.
- With the help of another expert, I succeeded in ignoring @Scan2 altogether.
- I posted only a simplified version of my Query on the forum, without the codes relating to eliminating the
  need to enter something in @Scan2, so you may not be aware of my requirement.
- I hope you understand my reluctance. But I will try your suggestion nevertheless.
My Suggestion
I think using PCH1.VISORDER may be the solution.
If we select only those rows where visorder = 0, then
   - there will be no duplication
   - I need not use SELECT DISTINCT
   - All my LINKS to pdf files will be live because I need not use CAST
   - I may retain that part of my Query which permits ignoring @Scan2 altogether.
- A Dream!-
The problem is that I don't know how and where  to place that VISORDER.
If you think I may be right, could you help me along that line?
Best Regards
Leon Lai