Parallel Query: Use temporary work tables to ship results: basic test

Current idea about shipping results from worker threads to the main thread is to use temporary (work) tables.

In a situation with N workers:
The primary thread creates N temporary tables, passes them over to the workers (each gets its own).
Each worker writes the results of its query portion into its temporary table.
Then, it notifies the primary thread that it is done.
After that, the worker doesn't access the table anymore.
The primary thread reads the data from the temp table and either does further processing or just sends it back to the client.