Are SQLite result sets in-memory data structures?

I currently find myself needing to do fairly simple computations on several million datapoints. (Constructing a large list of strings from a well defined multi-gigabite file, sorting that list, and then comparing it to another list, a superset.) This is the sort of simple work most of us normally do with the data entirely in-memory, but the size and quantity of the units of data I need to work with could make RAM an issue if I try to keep everything in memory. I quickly realized I probably need to write the data to a file, at a few points, to avoid exhausting my system's resources. I decided to use SQLite3 for this. (This is probably a bit much for a CSV.) It is fairly lightweight, while its storage limits seem to safely exceed my requirements.

The problem I am having is the understanding exactly how the result set works. The documentation I have come across seems a little vague on this. Obviously, SQLite is not writing a whole new table to the database every time a SELECT statement is executed. Does this mean it is duplicating all the selected fields in a complete in-memory table, or does it only keep some sort of pointers in memory (rather than the actual data)? Something else altogether?

I need to be able to sort the data in question. If the result set is really just an in-memory data structure, than simply creating creating a new table and populating it with the help of ORDER BY could be a bad idea.