I'm about to start a personal project and I'd love to use XTDB, but I'm not quite sure I should use it instead of a SQL db like eg. Postgres. The reason why I'm not sure is that I don't know if I'll be able to write complex queries in Datalog that I'd otherwise with SQL. I know this is kind of an open-ended question, but is it possible to write complex queries with joins and aggregations in Datalog? Or perhaps a better question is, what are the things that Datalog cannot do that SQL can?