title: append string to variable in a grafana query?
body: <p>In Grafana I have a drop down for variable $topic with values "topic_A" "topic_B"</p>
  
  <p>"topic_A" is selected so $topic = "topic_A"</p>
  
  <p>I want to query prometheus using</p>
  
  <pre><code>function{topic=$topic}
  </code></pre>
  
  <p>and that works fine.</p>
  
  <p>How would I implement </p>
  
  <pre><code>function{topic="$topic" + "_ERROR"}
  </code></pre>
  
  <p>(this fails) where what I want to query would be "topic_A_ERROR" if "topic_A" is selected.</p>
  
  <p>How do I combine variable $topic and string "_ERROR" in the query?</p>