Associating special meaning with user id 0

Question

I'm writing a plugin that creates a custom table holding data which is linked to a user account with a user_id field. Now if that users account would be deleted for any reason I would like to set that user_id field in my custom table to 0 to keep the stored data in an anonymized fashion.

Since the first user ID is 1 and counted upwards from there I would assume this is save. Is there any reason why this might have unwanted side effects?

Also, if I would add key constraints to my custom table this would obviousle be a problem when 0 is not existent in wp_users. Would it be hazardous to add a fake user record with id 0 to wp_users?

Answer 1

I think I found the most semantic solution: If I want to relate a given row of data to "nowhere", NULL is the best value to reflect that. And it even works with constraints on the field!