SELECT p.product_id, p.model, p.manufacturer_id, pd.name, pd.description,(select concat(ptc.category_id) from `oc_product_to_category` as ptc where (ptc.product_id=p.product_id) limit 2)  as str_cat
FROM  `oc_product` AS p 
left join  `oc_product_description` AS pd on (pd.product_id=p.product_id)
WHERE p.product_id NOT 
IN (
SELECT product_id
FROM oc_product_attribute
) order by p.product_id

SELECT p.product_id, p.model, p.manufacturer_id, pd.name, pd.description,concat(select ptc.category_id from `oc_product_to_category` as ptc where (ptc.product_id=p.product_id) limit 2)  as str_cat
FROM  `oc_product` AS p 
left join  `oc_product_description` AS pd on (pd.product_id=p.product_id)
WHERE p.product_id NOT 
IN (
SELECT product_id
FROM oc_product_attribute
) order by p.product_id