I've just tried this for all users without the 'where' clause & the followers remained.
I just did it via phpmyadmin. Is that the right place to do it? Anything else I need to do?
(for info - post import into XF a lot of my users are followed or are following. We don't have a 'follow' system on our old platform so this may confuse a few members so I want all clearing out while I decide if it's a feature we're going to use or remove via add-on.)