SQL组只包含表中以前没有的不同条目

I am using SQL server 2008. I have a Users table that holds users and their relationship to the Proposals in the system. Each user recorded is added to the system when a user is assigned to a Proposal. A User can show more than once in the Users table. The PK is User + Proposal. I have several columns, but the ones of interest are the I am using SQL server 2008. I have a Users tabl