Mysql Allowed memory size of 67108864 bytes exhausted

    $db->query('TRUNCATE TABLE `advert-region_count`');

    $categories = $db->query('SELECT `id` FROM `category`')->fetch_assoc_array();
    $regions = $db->query('SELECT `id` FROM `user-region`')->fetch_assoc_array();

    for ($i=0; $i < count($categories); $i++) {
        for ($j=0; $j < count($regions); $j++) {
            $db->query('
                    INSERT INTO `advert-region_count`
                    SET `id_region` = ?i,
                        `id_category` = ?i,
                        `count` = (SELECT count(*) FROM `advert` AS `a` INNER JOIN `user` AS `u` on `a`.`advert_id_user` = `u`.`id`
                                    WHERE `a`.`advert_place_region` = ?i
                                    AND `a`.`advert_category` = ?i
                                    AND `a`.`advert_active` = 1
                                    AND (`u`.`id` > 0 and `u`.`user_active` = 1 OR `u`.`id` = -1))',
                    $regions[$j]['id'], $categories[$i]['id'], $regions[$j]['id'], $categories[$i]['id']);
        }
    }