title: How to query location every 15 mins?
body: <p>I have a QuestDB table with item locations similar to the taxi trip database on the QuestDB Live demo and I want to query location but no more than every X mins per item. Similar query on the <a href="https://demo.questdb.io" rel="nofollow noreferrer">demo server</a> would be</p>
  <pre><code>SELECT vendor_id, pickup_latitude, pickup_longitude 
  FROM trips 
  WHERE vendor_id = 'VTS' 
  SAMPLE BY 15m
  </code></pre>
  <p>but get back error</p>
  <p><code>at least one aggregation function must be present in 'select' clause</code></p>
  <p>I don't want any aggregation like average etc, I just need the location every hour (or X mins). Is there a way to query that?</p>