مشکل با یک دستور sql در C#‎‎.Net

[hesampersian]

سلام دوستان

من یک دستور بصورت زیر نوشتم :

SELECT DISTINCT 

                         SellsTable.SellID, SellsTable.SellName, SellsTable.CustomerID, SellsTable.StartDate, SellsTable.EndDate, SellsTable.LastChangeDate, SellsTable.LastStateID, 

                         SellsTable.UserID, CustomerTable.CustomerName, CustomerTable.Mobile, CustomerTable.CustomerID AS Expr1, SellsTable.Balance, 

                         SUM(FactorProductTable.Count) AS Expr2

FROM            CustomerTable INNER JOIN

                         SellsTable ON CustomerTable.CustomerID = SellsTable.CustomerID INNER JOIN

                         FactorTable ON SellsTable.SellID = FactorTable.SellID INNER JOIN

                         FactorProductTable ON FactorTable.FactorID = FactorProductTable.FactorID

دستور مهم نیست مهم این خط هست SUM(FactorProductTable.Count) AS Expr2

که وقتی این اضافه میشه اررور زیر داده میشه

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Microsoft Visual Studio

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SQL Execution Error.



Executed SQL statement: SELECT DISTINCT SellsTable.SellID, SellsTable.SellName, SellsTable.CustomerID, SellsTable.StartDate, SellsTable.EndDate, SellsTable.LastChangeDate, SellsTable.LastStateID, SellsTable.UserID, CustomerTable.CustomerName, CustomerTable.Mobile, CustomerT...

Error Source: .Net SqlClient Data Provider

Error Message: Column 'SellsTable.SellID' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

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