Yes, you got that right! If you drop a foreign key constraint from a child table, and then follow up to INSERT/DELETE rows on parent and child in such way that is incompatible with foreign key constraints, and then revert, then the child, now again with the foreign key constraint, can have orphaned rows. It's as if you did `SET FOREIGN_KEY_CHECKS=0` and manipulated the data unobstructed. The schema itself remains valid, and some rows do not comply.
It's worth noting that MySQL has no problem with this kind of situation. It never cares about the existence of orphaned rows. It only cares about not letting you creating them in the first place, and it cares about cleaning up. But it doesn't blow up if orphaned rows do exist. They will just become ghosts.
It's worth noting that MySQL has no problem with this kind of situation. It never cares about the existence of orphaned rows. It only cares about not letting you creating them in the first place, and it cares about cleaning up. But it doesn't blow up if orphaned rows do exist. They will just become ghosts.