How to design database for personalized voting

I wonder how to create something like is doing twitter, but in relational databases.

One application of FlockDB that Weil cites is deter开发者_运维百科mining which users to show @ replies to. For example, if Ashton Kutcher sends a tweet to @foursquare, it shouldn't show up for all of Kutcher's 6,156,915 followers. It should show up only for users that follow both Kutcher and Foursquare.

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It has nothing to do with database design, but with how you query the database.

You definitely store each @follow at separate table, there you will have fields who tweets and who is replied. Than you will show the user X all @follows, in which both tweeting and replied is in set of people who he follows :)