黑马程序员——连接多次打开效率问题

1.比较下面代码，两段代码执行时间差不多，代码一中使用了连接复用（每次并不是真正关闭，连接池）
    1）每插入一条数据，连接打开“关闭”
     string[] telNum = File.ReadAllLines(ofd.FileName, Encoding.Default).ToArray();
    //            for (int i = 1; i < telNum.Count(); ++i)
    //            {
    //                string[] strs = telNum[i].Split('\t');//Tab键转义为“\t”
    //                string telnum = strs[0];
    //                string telarea = strs[1];
    //                string teltype = strs[2];
    //                string areanum = strs[3];
    //                SqlHelper.ExecuteNonQuery(sql,
    //                    new SqlParameter("@TelNum", telnum),
    //                    new SqlParameter("@TelNumArea", telarea),
    //                    new SqlParameter("@TelNumType", teltype),
    //                    new SqlParameter("@AreaNum", areanum));
    //            }


    2）一次打开，插入完成再关闭
     string[] telNum = File.ReadAllLines(ofd.FileName, Encoding.Default).ToArray();
            using (SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=stu;User ID=sa;Password=tao201415shu"))
            {
                conn.Open();
                using(SqlCommand cmd=conn.CreateCommand())
                {
                   
                    
                    for (int i = 1; i < telNum.Count(); ++i)
                    {
                        string[] strs = telNum[i].Split('\t');//Tab键转义为“\t”
                        string telnum = strs[0].Trim('"');
                        string telarea = strs[1].Trim('"');
                        string teltype = strs[2].Trim('"');
                        string areanum = strs[3].Trim('"');
                        //cmd.Parameters.Add(new SqlParameter("@TelNum", telnum));
                        //cmd.Parameters.Add(new SqlParameter("@TelNumArea", telarea));
                        //cmd.Parameters.Add(new SqlParameter("@TelNumType", teltype));
                        //cmd.Parameters.Add(new SqlParameter("@AreaNum", areanum));
                        //AddParams(cmd, strs);
                        sql = "insert into T_TelNumSearch(TelNum,TelNumArea,TelNumType,AreaNum)values('"+telnum+"','"+telarea+"','"+teltype+"','"+areanum+"')";
                        cmd.CommandText = sql;
                        cmd.ExecuteNonQuery();
                    }
                }
            }