/**
* Init collection select
*
* @return $this
*/
protected function _initSelect()
{
parent::_initSelect();
$connection = $this->getConnection();
$lastDate = $this->date->gmtTimestamp() - $this->visitorModel->getOnlineInterval() * self::SECONDS_IN_MINUTE;
$this->getSelect()->joinLeft(['customer' => $this->getTable('customer_entity')], 'customer.entity_id = main_table.customer_id', ['email', 'firstname', 'lastname'])->where('main_table.last_visit_at >= ?', $connection->formatDate($lastDate));
$expression = $connection->getCheckSql('main_table.customer_id IS NOT NULL AND main_table.customer_id != 0', $connection->quote(Visitor::VISITOR_TYPE_CUSTOMER), $connection->quote(Visitor::VISITOR_TYPE_VISITOR));
$this->getSelect()->columns(['visitor_type' => $expression]);
return $this;
}