On the one occasion I messed up the database update (no where clause ...) and needed to roll back, I got to learn about MySQL's binary log files. With a bit of messing, you can restore a known date old dump of your table, then run the bin log file data forwards (on just that table) to the last thing before you broke it all. The key requirement is that you have a database dump which is newer than the old end of your binary logs (assuming you have some mechanism for managing server binlogs, and access to them).