Duplicated Data Display

Hi all. i have the following function below,which use to retrieve the order detail from 2 table which are order detail and product. i have many duplicated order id in order detail, and each order id has a unique product id which link to product to display the product information. however when i run the following function below . its duplicated each product info and dsplay in the combo box. May i know whats wrong with my code?

    Public Sub ProductShow()

        Dim myReader As SqlCeDataReader
        Dim mySqlCommand As SqlCeCommand
        Dim myCommandBehavior As New CommandBehavior
        Try
            connLocal.Open()
            mySqlCommand = New SqlCeCommand
            mySqlCommand = connLocal.CreateCommand
            mySqlCommand.CommandText = "SELECT * FROM Product P,orders O,orderdetail OD WHERE  OD.O_Id='" & [Global].O_Id & "' AND P.P_Id=OD.P_Id "
                      myCommandBehavior = CommandBehavior.CloseConnection
            myReader = mySqlCommand.ExecuteReader(myCommandBehavior)
            While (myReader.Read())
                cboProductPurchased.Items.Add(myReader("P_Name").ToString())
            End While
            myReader.Close()
        Catch ex As Exception
            MsgBox(ex.ToString)
        Finally
            connLocal.Close()
        End Try

    End Sub