You can. First, find or implement a library in your language of choice to store indexed data on disk. Then implement some very hairy logic to make sure your rea

You can. First, find or implement a library in your language of choice to store indexed data on disk. Then implement some very hairy logic to make sure your read and write operations are ACID. Then choose an algorithm for the query you'd like to write. And then write it. I don't intend to be glib, but rather to illustrate some of the benefits of a database platform like modern RDBMSes. These things are all implemented and battle-tested for you. If you would prefer a more fine-grained control over execution of queries, you could probably get very far by starting with the SQLite code base and working at a more primitive level through its library.