SQL 服务器中的最后一个值选择

我正在尝试从SQL Server数据库中选择数据表中列的最后一个值。

我的代码是

private void bind_chart()
        {
            // here i am using SqlDataAdapter for the sql server select query
            SqlDataAdapter adp = new SqlDataAdapter("select last() * from Test", con);
            // here am taking datatable
            DataTable dt = new DataTable();
            try
            {
                // here datatale dt is fill wit the adp
                adp.Fill(dt);
                // this string m catching in the stringbuilder class
                // in the str m writing same javascript code that is given by the google.
                // my data that will come from the sql server
                // below code is same like as google's javascript code
                str.Append(@" <script type='text/javascript'>
                        google.load('visualization', '1', {packages:['gauge']});
                        google.setOnLoadCallback(drawChart);
                        function drawChart() {
                        var data = new google.visualization.DataTable();
                        data.addColumn('string', 'Label');
                        data.addColumn('number', 'Value');");
                // inside the below line dt.Rows.Count explain that
                // how many rows comes in dt or total rows
                str.Append("data.addRows(" + dt.Rows.Count + ");");
                Int32 i;
                for (i = 0; i <= dt.Rows.Count - 1; i++)
                {
                    // i need this type of output "  data.setValue(0, 0, 'Memory'); so on  in the first line so for this
                    //m using i for the 0,1& 2 and so on . and after this i am writting zero and after this student_name using datatable
                    str.Append("data.setValue( " + i + "," + 0 + "," + "'" + dt.Rows[i]["x"].ToString() + "');");
                    // i need this type of output "   data.setValue(0, 1, 80);
                    //so on  in the first line so for this
                    //m using i for the 0,1& 2 and so on . and after this i am writting zero and after this percentage using datatable
                    str.Append("data.setValue(" + i + "," + 1 + "," + dt.Rows[i]["y"].ToString() + ") ;");
                    //   str.Append("['" + (dt.Rows[i]["student_name"].ToString()) + "'," + dt.Rows[i]["average_marks"].ToString() + "],");
                }
                str.Append("var chart = new google.visualization.Gauge(document.getElementById('chart_div'));");
                // in the below line i am setting the height and width of the Gauge using your own requrirement
                str.Append(" var options = {width: 800, height: 300, redFrom: 90, redTo: 100,");
                //  str.Append(" var chart = new google.visualization.BarChart(document.getElementById('chart_div'));");
                str.Append("yellowFrom: 75, yellowTo: 90, minorTicks: 5};");
                str.Append("chart.draw(data, options);}");
                str.Append("</script>");
                lt.Text = str.ToString().TrimEnd(',');
            }
            catch
            {
            }
            finally
            {
            }
        }

并希望在仪表上显示最后一个值。在这里，我没有从生成的查询中获取最后一个值。我不知道为什么。