Learning plans, courses and users - join issue

Summary

Cannot add the last join that would avoid a cartesian product

Content

Dear All,

I'm trying to create a report that will allow the user to select a set of learning plans, and that should display all the courses attached to these plans, all users attached to these learning plans/courses, and the status of these courses.
The users are all assigned by the admins to the learning plans. The goal of the report is to show, amongst other things, how many users have not started the courses yet (compliance courses). If a user has not started a course in a given learning plan, he should have a row in the report (with blank details at the course level).