That would never work though, at least not in the perfect, non leaky way the author and you would like. When you have a loop, even if the database could somehow

That would never work though, at least not in the perfect, non leaky way the author and you would like. When you have a loop, even if the database could somehow understand that loop, you can put anything inside it. You could make a call to an outside service, write to disk, etc. With a single SQL query the database can take it and optimize it since it has a full understanding of its data domain.