Trigger for deleting rows by checking the length of dynamically created table size

[Preethi K]

I have a fixed length table(purchased) which is updated by a dynamically created table(cart).
i want to give a trigger to purchased in such a way that if the purchased table length meets its maximum size it should delete the oldest data in it to let insert the new data.
I'm stuck at the point of how many rows to delete before inserting into the table, because i will be copying the whole contents of cart table which is created dynamically, whose size is unpredictable.
any help would be appreciated