SELECT 
  product.product_id AS product_id, 
  product.company_id AS company_id, 
  descr.product, 
  SUM(sales.amount) AS amount 
FROM 
  cscart_products AS product 
  LEFT JOIN cscart_product_descriptions descr ON product.product_id = descr.product_id 
  LEFT JOIN cscart_product_sales AS sales ON product.product_id = sales.product_id 
WHERE 
  product.status = 'A' 
GROUP BY 
  product.product_id 
ORDER BY 
  amount DESC, 
  product.product_id ASC 
LIMIT 
  0, 4