-- =============================================================================
-- MIGRATION 004: Add course_id to levels
-- PURPOSE: Links each level to a course. Supports multiple courses.
-- =============================================================================

ALTER TABLE public.levels
    ADD COLUMN IF NOT EXISTS course_id INT REFERENCES public.courses(course_id);

-- Assign all existing levels to the default course
UPDATE public.levels SET course_id = 1;

-- Enforce NOT NULL once all rows are assigned
ALTER TABLE public.levels ALTER COLUMN course_id SET NOT NULL;