Yes it'd be safe to run the query.

I'm finding on my forums that i hvae some users who are '-1' and some who are ''; i'm thinking that When created they are created with '' and when they update their profile for the first time, it's changed to '-1'... I have nothing to back this, but it makes sense why one or two "new" users are '-1' whereas 20 other new users are ''...

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