I decided to replace my XAMPP folder with a new download so that I could get a later PHP version. Before doing that, I saved my htdocs and ./mysql/data sub-folders. After installing the latest version, I restored the subfolders, choosing not to overwrite new files with the same name.
When I went to run one of my sites by using localhost, I received the message "Error establishing a database connection."
Using phpmyadmin, I went to the database and got this message when I clicked a table: "#1932 - Table '***.***.***_options' doesn't exist in engine'. It was true for the other tables, too.
It looks like my replacement strategy didn't work as expected. I have quite a few databases and I'm wondering if and how it is possible to overcome this problem.