ci框架怎么读写操作mysql数据库

 ci框架中，怎么和数据库交互，下面是我写的简单示例函数：

function OprData(){

        $this->load->database();

        //返回多条记录

        $query = $this->db->query('select * from t_appinfo');

        if($query->num_rows()>0){

            foreach($query->result() as $row){

                echo "<br/>";

                echo $row->nID;

                echo $row->sAppName;

                echo $row->tTime;

            }

        }

        //插入数据

        $name='test';

        $sql = "insert into t_appinfo(sAppName,tTime) values(".$this->db->escape($name).",now())";

        $this->db->query($sql);

        echo "<br/>row:";

        echo $this->db->affected_rows();

        //返回单条记录

        $sql = "select * from t_appinfo order by ttime desc limit 1";

        $query = $this->db->query($sql);

        $row = $query->row();

        echo"<br/> time:".$row->tTime;

         //更新数据

        $sql = "update t_appinfo set sAppName='".$row->sAppName."11' where nid=".$row->nID;

        $query = $this->db->query($sql);

        echo "<br/>update row:";

        echo $this->db->affected_rows()."//".$query;

        //删除数据

        $sql="delete from t_appinfo limit 1 ";

         $query = $this->db->query($sql);

        echo "<br/>delete row:";

        echo $this->db->affected_rows()."//".$query;

    }