MySQL, repair a non-broken table Whenever a table crashes, MySQL returns as error: Table xxx crashed. Please repair the table.

Now I was wondering, what will happen if I repair a table that is healthy? Will it be ignored? Can I damage the table?

Reason: In the past days different tables have crashed and I'm considering issuing a repair on all tables as preventive measure.
Repairing a table that is not crashed shouldn't break anything in the ideal case. Unfortunately, the real world is not an ideal case; a power outage or a hardware failure during the repair can leave the table in an inconsistent state. That's why backing up the table before repairing it is strongly recommended.

Also having the database offline during the maintenance operations helps fixing it faster.

Please take a look at the documentation of REPAIR TABLE for more information.