Puedes hacer esto usando LEFT JOIN
:
SELECT b.Product,
b.Qty,
b.Price,
Result = CASE WHEN a.product IS NULL THEN 'New'
ELSE 'Updated: ' +
STUFF( CASE WHEN a.Qty != b.Qty THEN ',Qty' ELSE '' END +
CASE WHEN a.Price != b.Price THEN ',Price' ELSE '' END,
1, 1, '')
END
FROM TableB b
LEFT JOIN TableA a
ON a.Product = b.Product
WHERE a.Product IS NULL
OR a.Qty != b.Qty
OR a.Price != b.Price;