No, the pieces you downloaded can be reused for the new torrent download. The pieces will effectively have the same hash hence can be reused for the new digest: http://bittorrent.org/beps/bep_0038.html
This is also why sqlite is a good choice because it's highly optimized to do the least amount of changes to its "pieces" when an update occurs.
If you're implementing this behavior, trying to manage all kinds of different queries, building a querying engine on top of that, optimizing for efficiency and reliability, you're effectively rewriting a database. Sure you can do it, but why not take advantage of battle-tested off-the-shelf stuff for things like "databases" (sqlite) and/or "distributing data" (torrent)?
This is also why sqlite is a good choice because it's highly optimized to do the least amount of changes to its "pieces" when an update occurs.
If you're implementing this behavior, trying to manage all kinds of different queries, building a querying engine on top of that, optimizing for efficiency and reliability, you're effectively rewriting a database. Sure you can do it, but why not take advantage of battle-tested off-the-shelf stuff for things like "databases" (sqlite) and/or "distributing data" (torrent)?