The following SQL query return all rowsa instead from 12 to 18.
SELECT `reviews`.*,
`users`.`username` as `user_username`,
`users`.`slug` as `user_slug`
FROM `reviews`
JOIN `users` ON `users`.`id` = `reviews`.`user_id`
WHERE `reviews`.`product_id` = 2
ORDER BY `reviews`.`created_at` DESC LIMIT 12, 18
As result I have to get 6 rows instead all.