Is it a good idea/approach to index a VARCHAR column?
There's nothing wrong with indexing a varchar column if you're going to be doing queries based on it. However please keep in mind that there a limits to some indexes and how much they can index in a single field. Example you can't index a column that can contain an unlimited amount of text. However you should be able to do an index on varchar(256) without issue. Try it, and analyze the improvements in your queries performance to see if it helps.