c# DateTime oracle Date 插入

   DateTime datestart = this.dtmstartdata.Value;
   DateTime dateend = this.dtmenddata.Value;

string sql1 = "date_time  between  to_date('" + datestart.ToString("yyyy-MM-dd HH:mm:ss") + "','yyyy-MM-dd hh24:mi:ss') and to_date('" + dateend.ToString("yyyy-MM-dd HH:mm:ss") + "','yyyy-mm-dd hh24:mi:ss')";