$query = $this->db->query("SELECT p2c.product_id FROM `" . DB_PREFIX . "product_to_category` p2c 
LEFT JOIN `" . DB_PREFIX . "product` p ON (p2c.product_id = p.product_id) 
LEFT JOIN `" . DB_PREFIX . "product_to_store` p2s ON (p.product_id = p2s.product_id) 
WHERE p2c.category_id IN (" . $category_list . ") AND p2c.product_id != '" . (int)$product_id . "' AND p.status = '1' AND p.quantity > 0 AND p.date_available <= NOW() AND p2s.store_id = '0' 
ORDER BY RAND() 
LIMIT 8);

SELECT 
p2c.product_id 
FROM `oc_product_to_category` p2c 
LEFT JOIN `oc_product` p ON (p2c.product_id = p.product_id) 
LEFT JOIN `oc_product_to_store` p2s ON (p.product_id = p2s.product_id) 
WHERE 
p2c.category_id IN (42) 
AND p2c.product_id != '247' 
AND p.status = '1' 
AND p.quantity > 0 
AND p.date_available <= NOW() 
AND p2s.store_id = '0' 
ORDER BY 
RAND() 
LIMIT 8

SELECT 
p2c.product_id 
FROM `oc_product_to_category` p2c 
LEFT JOIN `oc_product` p ON (p2c.product_id = p.product_id) 
WHERE 
p2c.category_id IN (42) 
AND p2c.product_id != '247' 
AND p.status = '1' 
AND p.quantity > 0 
ORDER BY 
RAND() 
LIMIT 8

SELECT 
p2c.product_id 
FROM `oc_product_to_category` p2c 
LEFT JOIN `oc_product` p ON (p2c.product_id = p.product_id) 
WHERE 
p2c.category_id IN (42) // выбираем товары у которых категория 42
AND p2c.product_id != '247' // исключаем из списка товар который открыт
AND p.status = '1'  // товар включен
AND p.quantity > 0 // товар в наличии
ORDER BY 
RAND() 
LIMIT 8

SELECT 
p2c.product_id 
FROM `oc_product_to_category` p2c 
LEFT JOIN `oc_product` p ON (p2c.product_id = p.product_id) 
WHERE 
p2c.category_id = '42' // выбираем товары у которых категория 42
AND p2c.product_id != '247' // исключаем из списка товар который открыт
AND p.status = '1'  // товар включен
AND p.quantity > 0 // товар в наличии
ORDER BY 
RAND() 
LIMIT 8