I have made some unfortunate UPDATE on a Postgresql table. Is it possible to reverse that change without any backup / rollback save etc?
You could restore it by dropping the table (make sure link from other tables aren't connected to it) and applying the SQL script that was created before you made the update. In other words, use the previous script and apply it. If you don't have a previous script, start writing it out so it is exactly the way the table was before you applied this 'unfortunate' update. Good luck!