mir3 only has very basic sql querying abilities it doesnt allow you to do lists, limits, order things by asc or desc etc etc. you can write an external php script and set it up on a crontab to move the data to a custom sql table that does whatever query you want, in your case you would want a desc, limit 0, 1. and then set your npc to get that single data point you wanted setup in the custom sql table. the only trouble will be that the data wont be instantaneous, would be 1-2 seconds old, but meh
. but its not too difficult to do.