$res = M('video_cat')->alias('vc')
->field('cat_name')
->join('left join __CATEGORY__ c on vc.cat_id = c.id')
->where(['vc.video_id' => $video_id])
->limit(1)
->cache('videoCate_'.$video_id)
->select();


返回的数据{

"status": 0,
"message": "1103:Incorrect table name ''\n [ SQL语句 ] : SELECT `data`,`datacrc` FROM `` WHERE `cachekey`='api_videoCate_359' AND (`expire` =0 OR `expire`>1465298648) LIMIT 0,1",
"content": null

}