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;
}