如何避免telerik radcombobox中的重复值？

Question

我正在使用telerik Radcombobox。我正在使用radcombobox itemsrequestd事件处理程序。

Private Sub cbocompanyname_ItemsRequested(sender As Object, e As Telerik.Web.UI.RadComboBoxItemsRequestedEventArgs) Handles cbocompanyname.ItemsRequested
    Dim combo As RadComboBox = DirectCast(sender, RadComboBox)
    If e.Text <> "" Then
        objdbconn.OpenConn()
        Dim sql As String = "Select distinct company_gid, company_name from company_details WHERE company_name LIKE '%" + e.Text + "%'"
        Dim dt As New DataTable()
        dt = objdbconn.GetDatatable(sql)
        objdbconn.CloseConn()
        For Each row As DataRow In dt.Rows
            Dim item As New RadComboBoxItem(row("company_name").ToString())
            combo.Items.Add(item)
        Next
    End If
End Sub

这是我的Telerik RadCombobox设计：

<telerik:RadComboBox ID="cbocompanyname" runat="server" Width="75%" MaxLength="256" ShowToggleImage="false" Skin="WebBlue"
                                    EmptyMessage="Select Company Name/Individual Name" ItemsPerRequest="50" AllowCustomText="true" EnableLoadOnDemand="true" ZIndex="100000">
                                </telerik:RadComboBox>

我在这里检查公司名称是否已经存在。

 msSQL = "Select company_gid from company_details where company_name = '" & Replace(Trim(cbocompanyname.Text), "'", "'") & "'"
    objdatatable = objdbconn.GetDatatable(msSQL)
    If objdatatable.Rows.Count > 0 Then
        objdbconn.CloseConn()
        lblErrMsg.Text = "Company name already exists"
        Exit Sub
    End If

这是编辑页面。所以现在我想知道如何检查并添加公司名称。