[1055 Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'kado_site.product.product_id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by 
 select product_id,count(*) as nb_of_product,product_img,product_desc from product where category_id='12' group by category_id]