"When to index" isn't a question of the query. Not really. It's a question of what you're trying to do.
There's no way to tell, from what you wrote, wether you should index something or not.
Start out with a book on performance tuning. Read online articles on it, too, but pick out a good book as a first step.
- Gus "GSquared", RSVP, OODA, MAP, NMVP, FAQ, SAT, SQL, DNA, RNA, UOI, IOU, AM, PM, AD, BC, BCE, USA, UN, CF, ROFL, LOL, ETC
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"Nobody knows the age of the human race, but everyone agrees it's old enough to know better." - Anon