title: Can I conditionally add a where() clause to my knex query?
body: <p>I want to add a <code>where()</code> clause in my query, but <strong>conditionally</strong>. Specifically, I want it added only if a sepecific querystring parameter is passed in the URL. Is this possible, and if so, how would I go about doing it?</p>
  
  <pre><code>router.get('/questions', function (req, res) {
      knex('questions')
          .select('question', 'correct', 'incorrect')
          .limit(50)
          .where('somecolumn', req.query.param) // &lt;-- only if param exists
          .then(function (results) {
              res.send(results);
          });
  });
  </code></pre>