[Docs]: example for union #181

$select = $this->db('prefixed', 'prefix_')
            ->select('*')
            ->from('table AS u')
            ->where('type', 'user')->orWhere('table.id', '<', 100);

        $select->union(
            $this->db('prefixed', 'prefix_2_')
                ->select('*')
                ->from('table AS u')
                ->where('type', 'admin')->orWhere('table.id', '>', 800)
        );