To check I understand correctly, you want to display the Course Groups where a user has a certain role within one of the courses?
This is possible, but the
database relationships for achieving this are fairly complex. You can actually achieve this with the existing course categories structure, but you say you dont want to do that, so you might be doing something more that I've understood.
You'll want to look at the following tables and understand the relationships between then (assuming you're using the default mdl_ prefix):
mdl_course
mdl_course_categories
mdl_context
mdl_role_assignments
mdl_role
mdl_user
Don't try adding an field like "IDCourseGroup" to the core mdl_course table, or indeed modifying the core tables at all - this is asking for trouble. If you want to link courses to your own mdl_course_group table, have an interim table like "mdl_course_group_courses" that associates ids from mdl_course with ids from your mdl_course_group table.
