Most version control tools operate on the local disk file system.
Database objects for most relational database systems
We use Red Gate to compare current schema against the scripted files stored in SVN for baselines, versioning etc
However, our master reference is actually a restored copy of production. This is our baseline and should correspond to SVN. It's part of deployment process to commit the master scripts to SVN, which Red Gate does usefully: it only changing the files for changed objects.
We further separate our working scripts and release scripts (changes only), so we always have a master DB and a baseline in SVN. We only use scripts for development though.
Database source control is good stuff, but it's challenging to implement because of the nature of what a SQL Server object is: a row or 3 in some tables...