To make story short, i'm building self-learning banner management system. Users will be able to insert these banners to their site when banners will be shown based on sales/impressions ratio.

I have 4 tables

Banners 
bannerID      int
bannerImage   varchar....

SmartBanners
smartBannerID      int
smartBannerArrayID int
bannerID           int
impressionsCount   int
visibility         tinyint (percents)

SmartBannerArrays 
smartBannerArrayID int
userID             int

Statistics
bannerID          int
saleAmountPerDay  decimal...

Each night i need to generate new "visibility" for each SmartBanner based on whole SmartBannerArray that same user has. So i need to get sum of impressions and sales for each bannerID in SmartBannerArray.

All comes to my mind is to use double cursor, one will loop thought SmartBannerArrays get needed values for sum of impressions and sales and then inner loop which will access each SmartBanner and change it's "visibility" percentage based on (sales/impressions)/(sumOfSales/sumOfImpressions)*100

Hope you get the picture...

Is there any other way to design better tables or not to use double cursor to avoid server overload ?