title: Count unique in group by - Google Query
body: <p>I have this table:</p>
  
  <pre><code>A B
  1 4
  2 5
  3 6
  1 4
  2 4
  3 4
  </code></pre>
  
  <p>How could I output:</p>
  
  <pre><code>A count
  1 1
  2 2
  3 2
  </code></pre>
  
  <p>i.e. count records with distinct value.</p>
  
  <p>I have read that in mysql I could do:</p>
  
  <pre><code>select A, count(distinct B) from table group by A
  </code></pre>
  
  <p>How can I transform this to Google Spreadsheet Query language?</p>