Question

Got two tables: users(id, column) and objects(user_id, column).
How to extract all users who don’t have any corresponding object?
I’m using MySQL.

Answer 1

Something like this should suffice, left outer join to keep all users then remove any which have a corresponding object.

Select * 
from
   users u left outer join
   objects o on u.[id] = o.user_id
where
   o.user_id is null