I got into the habit a long time ago of writing my where clause first and then generally writing the rest as a select clause. Then converting the select into a update or delete. I don't always do the select thing it depends on what part of the DB I am working on. If it is a pretty complex statement I tend to write the select just to make sure. I have a guy that is better than me at SQL but he still has not taken my advice and every now and then I hear cussing coming from down the hall. He is good at backing things up but his process takes a lot of time when he messes up. I prefer the ounce of prevention path.
I first write out a select that will show me the records I'm about to modify, then replace the select + fields with the update. And I try to keep modifying live databases using interactive SQL to an absolute minimum.
