ขอถามเรื่อง ทำไม vb.net gridview ถึง insert ค่าซ้ำหรือคะ

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
                    ShowFooter="True"
                    OnRowEditing="modEditCommand"
                    OnRowCancelingEdit="modCancelCommand"
                    OnRowUpdating="modUpdateCommand" OnRowCommand="myGridView_RowCommand"> 
        <Columns>
            <asp:TemplateField HeaderText="Type ">
                <EditItemTemplate>
                    <asp:TextBox class="textbox_tableblue" size="10" ID="name_rate" runat="server" Text='<%# Bind("Name_RefType") %>'></asp:TextBox>
                </EditItemTemplate>
                <ItemTemplate>
                    <asp:Label ID="Label1" runat="server" Text='<%# Bind("Name_RefType") %>'></asp:Label>
                </ItemTemplate>
                <FooterTemplate>
                    <asp:TextBox id="txtAddType" size="10" runat="server"></asp:TextBox>
                </FooterTemplate>
                <HeaderStyle BackColor="LightCyan" BorderColor="LightCyan" Width="150px" 
                    ForeColor="Black" />
                <ItemStyle BackColor="LightCyan" BorderColor="LightCyan" Height="25px" />
                <FooterStyle BackColor="LightCyan" BorderColor="LightCyan" Height="25px" />
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Rate">
                <EditItemTemplate>
                    <asp:TextBox class="textbox_tableblue" size="10"  ID="rate" runat="server" Text='<%# DataBinder.Eval(Container, "DataItem.Rate_Refund") %>'></asp:TextBox>
                </EditItemTemplate>
                <ItemTemplate>
                    <asp:Label ID="Label1" runat="server" Text='<%# Bind("Rate_Refund") %>'></asp:Label>
                </ItemTemplate>
                <FooterTemplate>
                    <asp:TextBox id="txtAddrate" size="10" runat="server"></asp:TextBox>
                </FooterTemplate>
                <HeaderStyle BackColor="LightCyan" BorderColor="LightCyan" Width="100px" 
                    ForeColor="Black" />
                <ItemStyle BackColor="LightCyan" BorderColor="LightCyan" />
                <FooterStyle BackColor="LightCyan" BorderColor="LightCyan" Height="25px" />
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Status">
                <EditItemTemplate>
                    <table class="tableblue">
                        <tr><td align="left">
                    <asp:RadioButtonList ID="rdlStatusEdit" runat="server" >
                       <asp:ListItem Value="1" Selected="True">use</asp:ListItem>
                       <asp:ListItem Value="0">not use</asp:ListItem>
                    </asp:RadioButtonList>
                    </tr></td>
                    </table>
                </EditItemTemplate>
                <ItemTemplate>
                    <asp:Label ID="Label1" runat="server" Text='<%# Bind("statusStr") %>'></asp:Label>
                </ItemTemplate>
                <FooterTemplate>
                  <table class="tableblue">
                    <tr><td align="left">
                    <asp:RadioButtonList ID="rdlStatus" runat="server" >
                       <asp:ListItem Value="1" Selected="True">use</asp:ListItem>
                       <asp:ListItem Value="0">not use</asp:ListItem>
                    </asp:RadioButtonList>
                    </td><td>
                    <asp:Button  class="Buttonblack" id="btnAdd" runat="server" Text="Add" CommandName="Add"></asp:Button>
                    </td></tr>
                    </table>
                </FooterTemplate>
                <HeaderStyle BackColor="LightCyan" BorderColor="LightCyan" Width="150px" 
                    ForeColor="Black" />
                <ItemStyle BackColor="LightCyan" BorderColor="LightCyan" />
                <FooterStyle BackColor="LightCyan" BorderColor="LightCyan" Height="25px" />
            </asp:TemplateField>
            <asp:CommandField ShowEditButton="True" HeaderText="Action" >

                <HeaderStyle BackColor="LightCyan" BorderColor="LightCyan" Width="50px" 
                    ForeColor="Black" />
                <ItemStyle BackColor="White" BorderColor="LightCyan" />
                <FooterStyle BackColor="LightCyan" BorderColor="LightCyan" Height="25px" />
            </asp:CommandField>
           
        </Columns>
    </asp:GridView>

  Sub loadgridview()
        SQL(0) = " select Name_RefType ,  Rate_Refund , case when status = '1' then 'Use' else 'Not Use' end as statusStr  from " _
               & " ( select ID_RefType , Name_RefType  , status from Refund_Type ) as t1 " _
               & " left outer join ( select ID_RefType , Rate_Refund from Refund_Rate) as t2 " _
               & " on t1.ID_RefType = t2.ID_RefType where status = '1'"

        DT = M1.GetDatatable(SQL(0))

        Try
            ViewState("data") = DT
            GridView1.DataSource = DT
            GridView1.DataBind()
        Catch ex As Exception
            GridView1 = Nothing
        End Try

    End Sub

    Sub modEditCommand(ByVal sender As Object, ByVal e As GridViewEditEventArgs)
        GridView1.EditIndex = e.NewEditIndex
        GridView1.ShowFooter = False
        loadgridview()
    End Sub

    Sub modUpdateCommand(ByVal s As Object, ByVal e As GridViewUpdateEventArgs)

        '*** nametype ***'
        Dim txtType As TextBox = GridView1.Rows(e.RowIndex).FindControl("name_rate")

        '*** rate ***'
        Dim txtRate As TextBox = GridView1.Rows(e.RowIndex).FindControl("rate")

        '*** status ***'
        Dim RadStatus As RadioButtonList = GridView1.Rows(e.RowIndex).FindControl("rdlStatusEdit")


        Dim rateDouble As Double = 0
        Double.TryParse(txtRate.Text, rateDouble)
        'alert(e.RowIndex)


        SQL(0) = " UPDATE Refund_Type SET Name_RefType = '" & txtType.Text & "' " _
                & " , Updated_Date = getDate() , Updated_By = 'who' , status = '" & RadStatus.SelectedValue & "' " _
                & " WHERE ID_RefType = " & (e.RowIndex + 1)

        M1.Execute(SQL(0))

        SQL(1) = "select * from Refund_Rate where ID_RefType = " & (e.RowIndex + 1)
        DT1 = M1.GetDatatable(SQL(2))

        SQL(2) = " UPDATE Refund_Rate SET Rate_Refund = '" & Round(rateDouble, 2) & "' , Created_Date = getDate() , " _
                & "Created_By = 'who' , Status = '" & RadStatus.SelectedValue & "' Where ID_RefType = " & (e.RowIndex + 1)

        M1.Execute(SQL(2))

        'objCmd = New OleDbCommand(strSQL, objConn)
        'objCmd.ExecuteNonQuery()

        alert("ดำเนินการเรียบร้อยแล้วค่ะ")

        GridView1.EditIndex = -1
        GridView1.ShowFooter = True

        loadgridview()

    End Sub

    Sub myGridView_RowCommand(ByVal source As Object, ByVal e As GridViewCommandEventArgs)

        '*** nametype ***'
        Dim txtType As TextBox = CType(GridView1.FooterRow.FindControl("txtAddType"), TextBox)

        '*** rate ***'
        Dim txtRate As TextBox = CType(GridView1.FooterRow.FindControl("txtAddrate"), TextBox)

        '*** status ***'
        Dim RadStatus As RadioButtonList = CType(GridView1.FooterRow.FindControl("rdlStatus"), RadioButtonList)


        Dim rateDouble As Double = 0
        Double.TryParse(txtRate.Text, rateDouble)
        'alert(Round(rateDouble, 2))

        If e.CommandName = "Add" Then
            If chkexistaddbt() = False Then
                Exit Sub
            ElseIf chkinputaddbt() = False Then
                Exit Sub
            ElseIf chkIsNumberaddbt() = False Then
                Exit Sub
            End If


            SQL(0) = " insert into Refund_Type " _
                    & " (  Name_RefType , Updated_Date , Updated_By , Status  ) " _
                    & " values ( '" & txtType.Text & "' , getdate() , 'kam' , '" & RadStatus.SelectedValue & "') "

            M1.Execute(SQL(0))

            SQL(1) = "select * from Refund_Type order by ID_RefType DESC"
            DT = M1.GetDatatable(SQL(1))

            Dim id_type As String = DT.Rows(0)("ID_RefType")
            Dim statusVar As String = DT.Rows(0)("Status")

            SQL(2) = " insert into Refund_Rate " _
                   & " (  ID_RefType , Rate_Refund , Created_Date , Created_By , Status  ) " _
                   & " values (  '" & id_type & "' , '" & Round(rateDouble, 2) & "' , getdate() , 'kam' , '" & statusVar & "') "

            M1.Execute(SQL(2))

            alert("ดำเนินการเรียบร้อยแล้วค่ะ")

            loadgridview()

        End If
    End Sub


    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        If Not Page.IsPostBack() Then
            loadgridview()
        End If

    End Sub