If you'd like an idea of how last unread is implemented rather well, check out the Dwarf Fortress forums on Bay12.
http://www.bay12forums.com/smf/
Never stop learning, even if it hurts. Ego bruises are practically mandatory as you learn unless you've never risked enough to make a mistake.
For better assistance in answering your questions[/url] | Forum Netiquette
For index/tuning help, follow these directions.[/url] |Tally Tables[/url]
Twitter: @AnyWayDBA