title: How to query multiple sheets and merge the data?
body: <p>I have 15 sheets that use the same template, for 15 different users. I would like to make a query on all the sheets, and display the result in a separate sheet:</p>
  
  <pre><code>=QUERY(Mona!A3:U300; "select A, D where C != ''")
  </code></pre>
  
  <p>Where <code>Mona</code> is the name of 1 of the 15 sheets.</p>
  
  <p>So what I need is to make this QUERY on all the sheets and show the result. The columns (A,D) should only occur once.</p>
  
  <p>How can I accomplish this?</p>