reseting the hook_update_n status of a module
FYI, in Drupal 8, the system table has been removed, and this information is now stored in the key_value table.

UPDATE key_value SET value='i:8000;' WHERE collection = 'system.schema' AND name = 'module_name';


(As noted above, the actual value should be less than the hook_update_N() you want to repeat, but higher than or matching the last update that does not need to be repeated.)