Updating a table based on condition

Question

I have a database having a staging_table. From this table, entries are added to other table named Profile. Whenever staging_table is updated, it checks whether all its entries are present in Profile, if any is not present, add it to profile. Till, here its fine. Now I want that even if an entry exists in Profile, there might be a condition where some fields in Profile have been changed. So also want those entries to get updated.

Requirement: I cannot use any flags or any other table to check for its update.

Should I compare all fields? But that is very in-efficient. Please tell me, what should be the most efficient method that I should follow to achieve this?

Thanks