I wish to delete all orders in my database. How can I do this?

Probably the fastest and safest way is to list the orders in the admin, then over on the right side, change the status to "deleted" while holding the "ctrl" key and all orders displayed will change, then click "UPDATE".
Once deleted, the order move to deleted status, but will remain there until, and only if, you click the button to clear deleted orders.

Thanks,
David