title: Add new row to database if it doesn't exist
body: <p>How can I only add a new user if it doesn't already exist? </p>
  
  <p>Here is how I'm currently inserting a new user into the database</p>
  
  <pre><code>assert(typeof details.username === 'string');
  db.execute("INSERT INTO user (??) VALUES (?)",
      [
          ['username'],
          [details.username]
  </code></pre>