SELECT i.item, name, total, brandname
FROM @tb_item i
JOIN @tb_brand b ON i.brand = b.brand
JOIN (SELECT item, SUM(quantity) total FROM @tb_quantity GROUP BY item) q ON q.item = i.item
SELECT i.item, name, total, brandname
FROM @tb_item i
JOIN @tb_brand b ON i.brand = b.brand
JOIN (SELECT item, SUM(quantity) total FROM @tb_quantity GROUP BY item) q ON q.item = i.item