Will my database be affected if I upgrade? (And will I be able to revert to previous version?)
Short Answer: Yes, as a general rule, the upgrade will make changes to your database!
This means it is very important to have a backup of your existing system (database and files) before performing an upgrade. This way, if something is not working as you wish with the new version, you will always be able to restore your previous version. Note: backups are generally a good idea! You should make some even when you don’t upgrade!
Exception to the rule
Only for minor upgrades (e.g., from version a.b.x to a.b.y like 4.1.3 to 4.1.7) will there be no changes to the database.
In that case, you can still run the install/upgrade script. Do not worry, if nothing needs to be done, it won’t do anything. But it will check that everything is in good order for you.
Note: even when performing minor upgrade, we still recommend that you make a backup first.