怎么样优化sql地统计语句，增涨运行速度？

case "01":

                case "03":

                case "05":

                case "07":

                case "08":

                case "10":

                case "12":

                    for (int d = 1; d <= 31; d++)

                    {

                        date = txtyear.Text + "-" + cobMonth.Text + "-" + d.ToString();

                        for (int t = 6; t <= 23; t++)

                        {



                            string QueryCT1 = "SELECT Count(*) FROM EM_RecBuf WHERE rectype = '1'AND ( Tdatetime BETWEEN '" + date + " " + t.ToString() + ":00:00' AND '" + date + " " + t.ToString() + ":59:59')";

                            string QueryCT2 = "SELECT Count(*) FROM EM_RecBuf WHERE rectype = '2'AND ( Tdatetime BETWEEN '" + date + " " + t.ToString() + ":00:00' AND '" + date + " " + t.ToString() + ":59:59')";

                            string QueryCT3 = "SELECT Count(*) FROM EM_RecBuf WHERE rectype = '3'AND ( Tdatetime BETWEEN '" + date + " " + t.ToString() + ":00:00' AND '" + date + " " + t.ToString() + ":59:59')";

                            string QueryCT4 = "SELECT Count(*) FROM EM_RecBuf WHERE rectype = '4'AND ( Tdatetime BETWEEN '" + date + " " + t.ToString() + ":00:00' AND '" + date + " " + t.ToString() + ":59:59')";

                            //string QueryCBS = "SELECT Sum(balance) FROM EM_RecBuf WHERE ( Tdatetime BETWEEN '" + date + " " + t.ToString() + ":00:00' AND '" + date + " " + t.ToString() + ":59:59')";



                            SqlCommand sqlcmd1 = new SqlCommand(QueryCT1, conn);

                            cct1 = int.Parse(sqlcmd1.ExecuteScalar().ToString());



                            SqlCommand sqlcmd2 = new SqlCommand(QueryCT2, conn);

                            cct2 = int.Parse(sqlcmd2.ExecuteScalar().ToString());



                            SqlCommand sqlcmd3 = new SqlCommand(QueryCT3, conn);

                            cct3 = int.Parse(sqlcmd3.ExecuteScalar().ToString());



                            SqlCommand sqlcmd4 = new SqlCommand(QueryCT4, conn);

                            cct4 = int.Parse(sqlcmd4.ExecuteScalar().ToString());



                            ccs = cct1 + cct2 + cct3 + cct4;



                            //SqlCommand sqlcmdCBS = new SqlCommand(QueryCBS, conn);

                            //cbs = sqlcmdCBS.ExecuteScalar().ToString();



                            string time = t.ToString();

                            //写入本地数据库

                            SaveTolocal(date,time,cct1,cct2,cct3,cct4,ccs);



                        }

                    };

                    break;