In postgresql testresults database, investigate how to query test results based on date of workitem

The grafana queries to the new db will be based on workitem started_on date. For example "show the flaky runs of test X in the last 6 months" means "for all test workitems that started in the last 6 months".

The tables (test_runs_raw, flaky_tests etc) that hold this information, do not hold the date that the workitem started, they only have the "workitem_n" id that links them to the workitems table with that date.

How to write such queries so that they perform well, without adding extra indices if possible?