[Olreich]

It’s almost never faster to do two queries. But DBs are complicated query engines with sophisticated compilers, so you have to go in and try to convince the compiler to optimize the way you want that will make the query fast. EXPLAIN_ANALYZE is your best friend for understanding what the compiler thinks is best. And then you can adjust the query to convince it that it should do something faster.

In this specific case, I’d bet that having the FROM and JOIN tables reversed would be enough to get even better performance than 2 queries: `SELECT * FROM os JOIN o …`.