5
Oh I think he is searching for something different.
If you want to update/synchronize the posts of a single user, after you setted it to a custom value directly in the database, you have to do the following.
Go to administration > system admin > edit user, select the user and choose "modify user".
Now you get all the data for this user. At the end of this page, there is the function for synchronizing the user posts. Simply click on that button and the user count should be up to date!