SELECT MIN(unique_fieldset) id 
FROM goods
INNER JOIN (SELECT brand, MIN(price) AS price, article
           FROM goods
           GROUP BY brand, article, price) topprice 
    ON  goods.brand = topprice.brand 
    AND goods.price = topprice.price
    AND goods.article = topprice.article;

SELECT *
FROM goods
INNER JOIN (SELECT MIN(unique_fieldset) id 
            FROM goods
            INNER JOIN (SELECT brand, MIN(price) AS price, article
                        FROM goods
                        GROUP BY brand, article, price) topprice 
                ON  goods.brand = topprice.brand 
                AND goods.price = topprice.price
                AND goods.article = topprice.article
            GROUP BY brand, price, article) min_id
    ON min_id.unique_fieldset = goods.unique_fieldset