存储用户标识列表的最佳方法

I'm working on a PHP/MySQL rating system right now. For the user to be able to rate the user has to log in. Each user has a unique "UID". There will be multiple rating instances on the website (one for every game, in my case) and I need an efficient way of storing a list of UIDs in a MySQL row (one MySQL row in the ratings table for each instance of the rating system) to keep a tally of who has voted. I'm working on a PHP/MySQL rating system right