Aggregation in dynamic pivot table in SQL Server 2012 - sql-server

Question

I have a table in SQL Server 2012 which has 5 million rows.
Table view is like this :
CustomerID ProdID FavouriteProduct
1 A A
1 A A
1 A A
1 B A
1 A A
1 A A
1 A A
1 B A
2 A C
2 AN C
2 G C
2 C C
2 C C
2 F C
2 D C
2 C C
As you can see there are so many different products.
I already wrote a query for that :
DECLARE #DynamicPivotQuery AS NVARCHAR(MAX)
DECLARE #ColumnName AS NVARCHAR(MAX)
--Get distinct values of the PIVOT Column
SELECT
#ColumnName = ISNULL(#ColumnName + ',','') + QUOTENAME(prodID)
FROM
(SELECT DISTINCT ProdID FROM Table) AS Prods
--Prepare the PIVOT query using the dynamic
SET #DynamicPivotQuery =
N'SELECT CustomerID, ' + #ColumnName + '
FROM table
PIVOT(count(CustomerID)
FOR ProdID IN (' + #ColumnName + ')) AS PVTTable'
--Execute the Dynamic Pivot Query
EXEC sp_executesql #DynamicPivotQuery
Normally, I expect count(*) or Count(SubID) would count the number of each products bought by each customer, but it doesn't. It says
Invalid Column name CustomerID
instead.

Answer 1

You can't count the CustomerId while selecting it, try this instead:
SET #DynamicPivotQuery =
N'SELECT CustomerID, ' + #ColumnName + '
FROM table
PIVOT(count(FavouriteProduct)
FOR ProdID IN (' + #ColumnName + ')) AS PVTTable'
You need a column to count, and CustomerId is not allowed since you are selecting it. If FavouriteProduct fails, I suggest you fake a column or find another column.
Since you have more columns than described, I modified query. Try this instead:
SET #DynamicPivotQuery =
N'SELECT CustomerID, ' + #ColumnName + '
FROM
(SELECT CustomerID, FavouriteProduct, ProdID FROM table) x
PIVOT(count(FavouriteProduct)
FOR ProdID IN (' + #ColumnName + ')) AS PVTTable'