You can use the command:
OPTIMIZE TABLE `w3t_Posts`
Substitute any of the tables (like w3t_Users) in that command.
You can also find many useful mysql queries for threads here:
https://www.ubbdev.com/forum/showflat.php/Number/94362<img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" />