Power Query allows you to merge (“join” in database terms) two tables together in a variety of different ways, including left and right anti joins. Unfortunately, as I found recently, anti joins don’t fold on SQL Server-related data sources, which can result in performance problems. Luckily there is a different way of doing anti joins that does fold.
An anti-join, by the way, is the type of thing you use when performing a NOT EXISTS operation: what is in driver table A that is not in lookup table B given some condition set?