yii2 mysql如何跨数据库联表查询？ [ 2.0 版本 ]

yii2 mysql如何跨数据库联表查询？
我这样写好像不行啊

 $query = (new Query())->from('vip as ccv');
        $query->leftJoin(\Yii::$app->get('db').'user as u','ccv.phone = u.user_mobile_phone');
        $query->leftJoin(\Yii::$app->get('db').'applet as uah','uah.user_id = u.user_id');
        $query->leftJoin(\Yii::$app->get('db').'grade as cvg','uah.level = cvg.vip_id');

        if (isset($condition['mobile']) && $condition['mobile'] != '') {
            $query->andWhere(['=', 'mobile', $condition['mobile']]);
        }