The column '638' was specified multiple times for 'PVT'. Pivot - sql

Question

I've the following SQL Query
Select Product_Id, [riy] AS [riy],
[eas] AS [eas]
FROM
(SELECT Product_Id, Store_Name, Quantity
FROM [Product_Stock] INNER JOIN Store on Store.Id = [Product_Stock].Stock_Id where Product_Id = 435) ps
PIVOT
(
SUM(Quantity)
FOR Store_Name IN
([riy],[EAST WAREHOUSE - eas])
) AS pvt
it gives the expected result.Giving me total quantity for locations riy and eas.
However, I want to dynamically get the Store names instead of manually specifying them.
this is what I've done.
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
SELECT #cols = STUFF((SELECT ',' + QUOTENAME([Product_Id])
FROM [Product_Stock]
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
SELECT #query =
'SELECT Product_Id FROM
(SELECT Product_Id, Store_Name, Quantity
FROM [Product_Stock] INNER JOIN Store on Store.Id = [Product_Stock].Stock_Id where Product_Id = 435) PS
PIVOT
(
SUM(Quantity)
FOR Store_Name in (' + #cols + ')
) AS PVT'
EXEC SP_EXECUTESQL #query
This gives me an error saying The column '638' was specified multiple times for 'PVT'.
How can i solve this problem?

Answer 1

Without knowing your actual data this is a blind flight, but I think you have two issues:
You must use DISTINCT to get each value only once
You are not concatenating the stores names but the IDs of your products
Try this
SELECT #cols = STUFF((SELECT DISTINCT ',' + QUOTENAME([Store_Name])
FROM [Product_Stock]
INNER JOIN Store on Store.Id = [Product_Stock].Stock_Id
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')

Answer 2

Just make sure the cols are DISTINCT
... STUFF((SELECT DISTINCT ','...

Answer 3

Thanks #Shnugo for pushing me in the right direction. Here's the query I finally ended up using.
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
SELECT #cols = STUFF((SELECT DISTINCT ',' + QUOTENAME([Store].Store_Name)
FROM [Store] INNER JOIN Product_Stock ON Product_Stock.Stock_Id = Store.Id
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
SELECT #query =
'SELECT Product_Id , ' + #cols + ' from
(SELECT Product_Id, Store_Name, Quantity
FROM [Product_Stock] INNER JOIN Store on Store.Id = [Product_Stock].Stock_Id WHERE Product_Stock.product_id = 435 ) PS
PIVOT
(
SUM(Quantity)
FOR Store_Name in (' + #cols + ')
) AS PVT'
EXEC SP_EXECUTESQL #query