DROP INDEX IF EXISTS idx_files_group;
DROP INDEX IF EXISTS idx_folders_group;
DROP INDEX IF EXISTS idx_folders_group_root_name;
DROP INDEX IF EXISTS idx_folders_group_name;

ALTER TABLE groups  DROP COLUMN IF EXISTS quota_bytes;
ALTER TABLE files   DROP CONSTRAINT IF EXISTS files_one_principal;
ALTER TABLE folders DROP CONSTRAINT IF EXISTS folders_one_principal;

-- Erst die Gruppendaten entfernen, sonst scheitert das NOT NULL unten.
DELETE FROM files   WHERE group_id IS NOT NULL;
DELETE FROM folders WHERE group_id IS NOT NULL;

ALTER TABLE files   DROP COLUMN IF EXISTS group_id;
ALTER TABLE folders DROP COLUMN IF EXISTS group_id;

ALTER TABLE files   ALTER COLUMN owner_id SET NOT NULL;
ALTER TABLE folders ALTER COLUMN owner_id SET NOT NULL;