Do some Excel Work

Hi, I have a large list of approx 20,000 names and addresses and email addresses, lets call that sheet A. I also have a sheet of email addressed and names only, lets call that sheet B. I need someone to ensure that all the names and email addresses from sheet B are in sheet A and if they are not already then they need to be inserted. It's basically combining two sheets and where there is duplicates, removing the dupe that he the least information. i don't want to delete any info from A at all unless there is a dupe.