ดึงข้อมูลใน Database มาโชว์ใน Combobox มันขึ้นแค่อันเดียว

 Sub Cbo_SElect()
        sql = "Select DISTINCT  WHCode, ShelfCode from BCStkIssueSub"
        da = New SqlDataAdapter(sql, cn)
        dt_WHCode = New DataTable
        da.Fill(dt_WHCode)
        Dim dr As DataRow = dt_WHCode.NewRow
        dr(0) = "--ระบุ--"
        dr(1) = "--ระบุ--"
        dt_WHCode.Rows.InsertAt(dr, 0)
        If dt_WHCode.Rows.Count > 0 Then
            With Cbo_WHCode
                .DataSource = dt_WHCode
                .DisplayMember = "WHCode"

            End With
        End If

        sql = "Select DISTINCT  WHCode, ShelfCode from BCStkIssueSub"
        da = New SqlDataAdapter(sql, cn)
        dt_ShelfCode = New DataTable
        da.Fill(dt_ShelfCode)
        Dim dr2 As DataRow = dt_ShelfCode.NewRow
        dr2(0) = "--ระบุ--"
        dr2(1) = "--ระบุ--"
        dt_ShelfCode.Rows.InsertAt(dr, 0)
        If dt_ShelfCode.Rows.Count > 0 Then
            With Cbo_ShelfCode
                .DataSource = dt_ShelfCode
                .DisplayMember = "ShelfCode"
            End With
        End If
    End Sub