I suddendly grabbed your precious trick !
Well; I would use the same SUM(IF()) or COUNT(IF()) constructs on tables like
post or
thread, to reduce the query count when I check for posts since a time, per user, and so on...
(note: I built indexes on those 'time' fields)
My question is: should a COUNT(IF()) clause much heavy than three or forur different SELECTS, on such a large tables ?
Thanks