JOIN方法是连贯操作中唯一可以多次调用的方法

分别查询表artist、work、card 、card
JOIN 有两种方式：LEFT JOIN（默认使用）与RIGHT JOIN
//Left Join
$Model->join('work ON artist.id = work.artist_id')->join('card ON artist.card_id = card.id')->select();


$Model->table('user U')->join('news N on U.id=N.cid')->field('U.*,N.*')->order('id desc')->limit('8')->select();

//Left Join
$Model->table('user U')->join('news N on U.id=N.cid')->field('U.*,N.*')->order('id desc')->limit('8')->select();

//Right Join
$Model->join('RIGHT JOIN work ON artist.id = work.artist_id')->select();

$Model->table('user U')->join(array('right','news N on U.id=N.cid'))->field('U.*,N.*')->order('id desc')->limit('8')->select();