Count of constituents who attended more than one performance in a production season

After nearly three weeks on vacation, my body is back but my brain has decided it needs a bit more time. :-) I know we've covered this before, but I can't find the thread. I've been asked for a count of people who attended a special exhibition more than one over its run -- a constituent count would suffice, but a ticket count would be great too. 

Thanks!
Anne Robichaux