select ProductID
,StockOnSite
,StockOffsite
,StockOnSite - StockOffsite
,cast(Stockonsite as varchar(10))+'/' +cast(StockOffsite as varchar(10))
from Products pr1
where StockOnSite - StockOffsite = (Select max(StockOnSite - StockOffsite)
from Products pr2
where pr1.ProductID = pr2.ProductID
)
group by ProductID, StockOnSite, StockOffsite