Introduction

So far, we have been interacting with Comma-Separated Values (CSV) files from disk and in memory with no persistence. Each time we restart our REPL, we lose all the data manipulation or ELO calculations we've made up to that point and must restart from scratch. If there were a means of persisting this state each time, we could begin where we left off last time. Indeed, we could imagine building an ELO calculation application with a web interface or even a ClojureScript frontend once we've established a means of persistent storage so that our progress is maintained from session to session.

When considering persistence, most applications will reach for a relational database implementation (for example, MySQL, Oracle, or PostgreSQL). There are many implementations to choose from, each with their own strengths and weaknesses.

We'll use Apache Derby as an on-disk Relational Database Management System (RDBMS). It is implemented entirely in Java, meaning...