попробуйте открыть файл \system\library\cart.php
и поменять местами блоки
$product_discount_query = $this->db->query("SELECT price FROM " . DB_PREFIX . "product_discount WHERE product_id = '" . (int)$product_id . "' AND customer_group_id = '" . (int)$customer_group_id . "' AND quantity <= '" . (int)$discount_quantity . "' AND ((date_start = '0000-00-00' OR date_start < NOW()) AND (date_end = '0000-00-00' OR date_end > NOW())) ORDER BY quantity DESC, priority ASC, price ASC LIMIT 1"); if ($product_discount_query->num_rows) { $price = $product_discount_query->row['price']; }
// Product Specials $product_special_query = $this->db->query("SELECT price FROM " . DB_PREFIX . "product_special WHERE product_id = '" . (int)$product_id . "' AND customer_group_id = '" . (int)$customer_group_id . "' AND ((date_start = '0000-00-00' OR date_start < NOW()) AND (date_end = '0000-00-00' OR date_end > NOW())) ORDER BY priority ASC, price ASC LIMIT 1"); if ($product_special_query->num_rows) { $price = $product_special_query->row['price']; }
по умолчанию они друг за другом, сделайте наоборот, второй первым
// Product Specials $product_special_query = $this->db->query("SELECT price FROM " . DB_PREFIX . "product_special WHERE product_id = '" . (int)$product_id . "' AND customer_group_id = '" . (int)$customer_group_id . "' AND ((date_start = '0000-00-00' OR date_start < NOW()) AND (date_end = '0000-00-00' OR date_end > NOW())) ORDER BY priority ASC, price ASC LIMIT 1"); if ($product_special_query->num_rows) { $price = $product_special_query->row['price']; }$product_discount_query = $this->db->query("SELECT price FROM " . DB_PREFIX . "product_discount WHERE product_id = '" . (int)$product_id . "' AND customer_group_id = '" . (int)$customer_group_id . "' AND quantity <= '" . (int)$discount_quantity . "' AND ((date_start = '0000-00-00' OR date_start < NOW()) AND (date_end = '0000-00-00' OR date_end > NOW())) ORDER BY quantity DESC, priority ASC, price ASC LIMIT 1"); if ($product_discount_query->num_rows) { $price = $product_discount_query->row['price']; }