在子查询中获取 DISTINCT 值

Question

I have a recently been trying to convert the First() function from MS Access to T-SQL. Now First() does not exist in T-SQL so I've had to explore some alternatives. I Found the First_Value function which seems to do the job.

However, Take the code below:

SELECT [Order Transactions Table].[Job Number],
   [Order Transactions Table].OutstandingBalance,
   [Order Transactions Table].[Accepted Quantity],
   MRPStockOut.MRPStockOutID,
   MRPStockOut.[Date],
   MRPStockOut.[Units],
   MRPHeader.MRPHeaderID,
   FIRST_VALUE(MRPSupplier.StockCode) OVER (PARTITION BY MRPSupplier.StockCode ORDER BY MRPSupplier.StockCode) AS FirstOfStockCode,
   --(SELECT TOP (1) MRPSupplier.StockCode ORDER BY [Order Transactions Table].[Job Number]) AS FirstOfStockCode,
   MRPHeader.MaterialDescription,
   MRPStockOut.StockQtyOut,
   MRPHeader.WeightPerUnit * MRPStockOut.StockQtyOut AS [Weight],
   LiveWIPStockAllocatedToJobsPrices.PurchPriceEach,
   LiveWIPStockAllocatedToJobsPrices.StockPriceEach,
   LiveWIPStockAllocatedToJobsPrices.PriceEach,
   (IIF(ISNULL(LiveWIPStockAllocatedToJobsPrices.PurchPriceEach,0) > 0,
    ISNULL(LiveWIPStockAllocatedToJobsPrices.PurchPriceEach,0),
    ISNULL(LiveWIPStockAllocatedToJobsPrices.StockPriceEach,0)) +0) * MRPStockOut.StockQtyOut AS TotalPrice

FROM [Order Transactions Table]
INNER JOIN MRPStockOut ON [Order Transactions Table].[Job Number] = MRPStockOut.JobNumber
INNER JOIN MRPHeader ON MRPStockOut.MRPHeaderID = MRPHeader.MRPHeaderID
INNER JOIN LiveWIPStockAllocatedToJobsPrices ON MRPHeader.MRPHeaderID = 
LiveWIPStockAllocatedToJobsPrices.MRPHeaderID
INNER JOIN MRPSupplier ON MRPHeader.MRPHeaderID = MRPSupplier.MRPHeaderID
GROUP BY
[Order Transactions Table].[Job Number],
[Order Transactions Table].OutstandingBalance,
[Order Transactions Table].[Accepted Quantity],
MRPStockOut.MRPStockOutID,
MRPStockOut.[Date],
MRPStockOut.[Units],
MRPHeader.MRPHeaderID,
MRPSupplier.StockCode,
MRPHeader.MaterialDescription, 
MRPStockOut.StockQtyOut,
MRPHeader.WeightPerUnit * MRPStockOut.StockQtyOut,
LiveWIPStockAllocatedToJobsPrices.PurchPriceEach,
LiveWIPStockAllocatedToJobsPrices.StockPriceEach,
LiveWIPStockAllocatedToJobsPrices.PriceEach,
(IIF(ISNULL(LiveWIPStockAllocatedToJobsPrices.PurchPriceEach,0) > 0,
ISNULL(LiveWIPStockAllocatedToJobsPrices.PurchPriceEach,0),
ISNULL(LiveWIPStockAllocatedToJobsPrices.StockPriceEach,0)) +0) * MRPStockOut.StockQtyOut
Having [Order Transactions Table].OutstandingBalance > 0

Particularly the line to select the first value in MRPSupplier. ( First(MRPSupplier.StockCode) in Access)

FIRST_VALUE(MRPSupplier.StockCode) OVER (PARTITION BY MRPSupplier.StockCode ORDER BY MRPSupplier.StockCode) AS FirstOfStockCode

Now this value is returning what that I am expecting, however, certain Jobs are come back with 2 records rather than one, under the same [Job Number]. This is because one of the duplicate jobs comes back with FirstOfStockCode = Null and the other has the expected value.

This is a problem because this is a subquery and I have a SUM on the query above which is giving me an incorrect because TotalPrice is being Summed twice due to the duplicate record. How can I get it so that I only receive a Distinct value from this column?

Edit:

Current Results:

Expected Results are the only the 2nd record above is selected the First NULL record shouldn't be in the select list.

Edit 2:

Here is another screenshot of more records (546 rows - This is two more than I get in MS Access):

Again, These two Null value records should not be exist as they are duplicates Edit 3: User @Isaac has managed to help me resolve this. See comments thread in his answer.

Answer 1

Try replacing this line...

FIRST_VALUE(MRPSupplier.StockCode) OVER (PARTITION BY MRPSupplier.StockCode ORDER BY MRPSupplier.StockCode) AS FirstOfStockCode,

with this...

FIRST_VALUE(MRPSupplier.StockCode) OVER (ORDER BY MRPSupplier.StockCode) AS FirstOfStockCode,

I believe The PARTITION BY clause is causing the extra row to be returned. If that causes the row with a NULL value to be returned add DESC like this...

FIRST_VALUE(MRPSupplier.StockCode) OVER (ORDER BY MRPSupplier.StockCode DESC) AS FirstOfStockCode,