(VB) ห้ามทำการ Update ข้อมูลที่ซ้ำกับข้อมูลใน Gridview (เชื่อมกับ sqlserver) ถ้าซ้ำให้เเสดงข้อความเตือน ทำยังไงค่ะ

 Private Sub GridView_promotion_RowUpdating(sender As Object, e As GridViewUpdateEventArgs) Handles GridView_promotion.RowUpdating

 Using sqlconn As New OleDbConnection(ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString)
            Dim cmd As New OleDbCommand()
            cmd.Connection = sqlconn

            cmd.CommandText = "UPDATE promotion SET  product = ?,min_price = ?, max_price = ?, discount = ? WHERE promotion_id = ?"
            cmd.CommandType = CommandType.Text

            Dim strpromotion_id As String = GridView_promotion.DataKeys(e.RowIndex).Item(0).ToString
            Dim a As TextBox = GridView_promotion.Rows(e.RowIndex).Cells(3).Controls(0)
            Dim strproduct As String = CType(GridView_promotion.Rows(e.RowIndex).Cells(3).Controls(0), TextBox).Text
            Dim strminP As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(4).Controls(0), TextBox).Text
            Dim strmaxP As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(5).Controls(0), TextBox).Text
            Dim strDis As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(7).Controls(0), TextBox).Text


            cmd.Parameters.Add("@p_product", OleDbType.VarChar).Value = strproduct
            cmd.Parameters.Add("@p_min", OleDbType.Decimal).Value = strminP
            cmd.Parameters.Add("@p_max", OleDbType.Decimal).Value = strmaxP
            cmd.Parameters.Add("@p_dis", OleDbType.Decimal).Value = strDis
            cmd.Parameters.Add("@p_id", OleDbType.Integer).Value = strpromotion_id
            sqlconn.Open()
            cmd.ExecuteNonQuery()
            sqlconn.Close()
        End Using


        GridView_promotion.EditIndex = -1
        BindGridView()
        lblAdd.Visible = True

    End Sub

 Private Sub GridView_promotion_RowUpdating(sender As Object, e As GridViewUpdateEventArgs) Handles GridView_promotion.RowUpdating


        Dim cap_promotion_id As Integer = GridView_promotion.DataKeys(e.RowIndex).Item(0).ToString
        Dim cap_productcode As String = CType(GridView_promotion.Rows(e.RowIndex).Cells(3).Controls(0), TextBox).Text
        Dim cap_min As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(4).Controls(0), TextBox).Text
        Dim cap_max As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(5).Controls(0), TextBox).Text
        Dim cap_dis As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(7).Controls(0), TextBox).Text


        If Not InsertProduct(cap_promotion_id, cap_productcode, cap_min, cap_max, cap_dis) Then
        Using sqlconn As New OleDbConnection(ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString)
            Dim cmd As New OleDbCommand()
            cmd.Connection = sqlconn

            cmd.CommandText = "UPDATE promotion SET  product = ?,min_price = ?, max_price = ?, discount = ? WHERE promotion_id = ?"
            cmd.CommandType = CommandType.Text

            Dim strpromotion_id As String = GridView_promotion.DataKeys(e.RowIndex).Item(0).ToString
            Dim a As TextBox = GridView_promotion.Rows(e.RowIndex).Cells(3).Controls(0)
            Dim strproduct As String = CType(GridView_promotion.Rows(e.RowIndex).Cells(3).Controls(0), TextBox).Text
            Dim strminP As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(4).Controls(0), TextBox).Text
            Dim strmaxP As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(5).Controls(0), TextBox).Text
            Dim strDis As Decimal = CType(GridView_promotion.Rows(e.RowIndex).Cells(7).Controls(0), TextBox).Text


            cmd.Parameters.Add("@p_product", OleDbType.VarChar).Value = strproduct
            cmd.Parameters.Add("@p_min", OleDbType.Decimal).Value = strminP
            cmd.Parameters.Add("@p_max", OleDbType.Decimal).Value = strmaxP
            cmd.Parameters.Add("@p_dis", OleDbType.Decimal).Value = strDis
            cmd.Parameters.Add("@p_id", OleDbType.Integer).Value = strpromotion_id
            sqlconn.Open()
            cmd.ExecuteNonQuery()
            sqlconn.Close()
        End Using


        GridView_promotion.EditIndex = -1
        BindGridView()
        lblAdd.Visible = True

        Else
            Response.Write("โปรโมชั่นซ้ำ ErrorXYZ ")
        End If


    End Sub
    Public Function InsertProduct(ByVal Promotionid As Integer, ProductCode As String, CapMin As Decimal, CapMax As Decimal, CapDiscount As Decimal) As Boolean

        Dim reader2 As OleDbDataReader
        Dim comm2 As String
        comm2 = " Select promotion_id "
        comm2 += " FROM promotion"
        comm2 += " where promotion_id = '" & Promotionid & "'"
        comm2 += " (select product ,min_price  ,max_price,discount  "
        comm2 += " FROM promotion "
        comm2 += " where product = '" & ProductCode & "' "
        comm2 += " and (( '" & CapMin & "'  >= min_price and '" & CapMin & "' <= isnull(max_price,99999999)) "
        comm2 += " or ('" & CapMax & "' >= min_price and '" & CapMax & "' <= isnull(max_price,99999999)))) "

        Dim OleComm2 As New OleDbCommand(comm2, sqlconn)
        sqlconn.Open()
        reader2 = OleComm2.ExecuteReader(CommandBehavior.CloseConnection)
        If reader2.HasRows Then
            Return False
        Else
            Return True
        End If
    End Function