Consider creating a unified Transactions and TransactionsDetails table – after all, Purchases means “stuff coming in and money going out”, while Sales is the exact reverse, so this boils more or less down to a difference in the sign you use.
Makes it much easier to create the time-dependent report you're trying to achieve, be it as a list or in a portal; you also just need one script to manage your stock levels (and for that matter, you just need one of everything …).
If you don't want or can't use such unified tables, investigate the “Virtual List” technique.
Thanks Friend erolst,
For your reply
Though I have already gone through solution demo file RunningInPortal_byRelationship_. But I just only want to browse the records from both the portals (Purchase Details and sale details) accordingly date wise in third portal table in sequence datewise. I do not want to make any transaction in third portal table.