Sometimes table scans happen even when you think you know what you're doing. If someone adds a column and doesn't think anyone will be filtered on that column then it can easily happen. I usually ask people:

- how big is this table getting? - how are you querying on it?

That usually fixes most problems before they happen. Not sure it's my job to specify a join type though. A nested loop join isn't a bad thing or even a sign of a bad thing happening necessarily.