title: mysql dataset with timestamp interval
body: <p>I have a dataset with timestamps and values like this:</p>
  
  <pre><code>Timestamp            Value
  "01-01-2017 09:01" , "900"
  "01-01-2017 09:28" , "770"
  "01-01-2017 09:55" , "240"
  "01-01-2017 10:36" , "850"
  "01-01-2017 11:01" , "820"
  </code></pre>
  
  <p>But what happens is that there is not always a measurement within 30 minutes, and I want to 'fill' this in with an extra row with null for value.
  Something like this:</p>
  
  <pre><code>Timestamp            Value
  "01-01-2017 09:01" , "900"
  "01-01-2017 09:28" , "770"
  "01-01-2017 09:55" , "240"
  "01-01-2017 10:00" , null     &lt;--
  "01-01-2017 10:36" , "850"
  "01-01-2017 11:01" , "820"
  </code></pre>
  
  <p>How can I do this?</p>
  
  <p>I'm using a Google Graphs line-graph with the 'function' parameter to make the line curve. When there is a gap in my measurements (=dataset) it should also show in the graph. Now it just connects all the dots to make a smooth line, so I need to add entries (timestamps) with a null value to create these gaps.</p>
  
  <p><a href="https://i.stack.imgur.com/stR8p.jpg" rel="nofollow noreferrer">Something like this</a></p>
  
  <p>Thanks in advance!</p>