Introduce subqueries to be used in condition statements, example:

"SELECT name FROM foo WHERE name NOT IN (SELECT name FROM ../bar WHERE date < ...)"

This shouldn't be too hard to implement.

First step is to introduce an IN operator for strings/numbers. The operator will return true if current the value is in the provided list.

The subquery should be evaluated individually. It returns a []Result for all files that passed the query (a Result struct holds each of the applicable attributes for a single file). Now we can apply IN to this result list.

Idea from https://news.ycombinator.com/item?id=14344493.