SELECT * FROM `client`
LEFT JOIN `user` ON `client`.`client_id` = `user`.`id`
LEFT JOIN `company` ON `user`.`company_id` = `company`.`id`
$dataProvider = new ActiveDataProvider([
'query' => Client::find()
->leftJoin('user', 'client.client_id = user.id')
->leftJoin('company', 'user.company_id = company.id')
]);