thinkphp 连表查询 join

public function getCanPinById($id)
{
$info = M("caipin")->alias("t1")
->join("left join my_category t2 on t1.categoryid=t2.id")
->field("t1.id,t1.title,t1.content,t1.price,t1.picture,t1.cai_unit,t2.cname")
->where(array('t1.id'=>$id))->find();
if($info)$info['picture'] = C('APP_PATH').$info['picture'];
return $info;
}