Conversion of scalar variable in query - sql-server

Question

I am working with public database Wide World Importers and I try to make some query.For input in this query I want to use scalar variables. You can see code below:
DECLARE #SupplierID int = 7
DECLARE #YearMonth NVARCHAR = '2013.1'
SELECT
pur.SupplierID, SUM(purst.TransactionAmount) AS TotalTransaction,
CONCAT(YEAR(pur.OrderDate), '.', MONTH(pur.OrderDate)) AS YearMonth
FROM
[Purchasing].[PurchaseOrders] AS pur
INNER JOIN
[Purchasing].[SupplierTransactions] AS purst ON purst.SupplierID = pur.SupplierID
WHERE
pur.SupplierID = #SupplierID
AND YearMonth = #YearMonth
GROUP BY
pur.OrderDate, pur.SupplierID
Above code work well and give me good result (but without scalar variable #YearMonth). You can see result below:
But when I try to include YearMonth like scalar variable into this query I get this error:
Msg 207, Level 16, State 1, Line 3831
Invalid column name 'YearMonth'
So can anybody help me how to fix this problem and make query properly?

Answer 1

You can't reference a column declared in the SELECT in the WHERE. You need to reference the actual columns in the table in the WHERE, or use a subquery or CTE.
What you should be doing here, however, is using proper date logic:
DECLARE #SupplierID int = 7,
#StartDate date = '20130101',
#EndDate date = '20130201';
SELECT PO.SupplierID,
SUM(ST.TransactionAmount) AS TotalTransaction,
CONCAT(YEAR(PO.OrderDate), '.', MONTH(PO.OrderDate)) AS YearMonth
FROM [Purchasing].[PurchaseOrders] PO
INNER JOIN [Purchasing].[SupplierTransactions] ST ON ST.SupplierID = PO.SupplierID
WHERE PO.SupplierID = #SupplierID
AND PO.OrderDate >= #StartDate
AND PO.OrderDate < #EndDate
GROUP BY PO.OrderDate,
PO.SupplierID;
I also change your aliases to something a bit more appropriate.