title: Query for counting how many times a value in one column exists in another column of the same table
body: <p>Table</p>
  
  <pre><code>id  A   B 
  1   3   5
  2   1   3
  3   7   8
  4   5   3
  5   2   5
  6   11  5
  </code></pre>
  
  <p>I want the result</p>
  
  <pre><code>A   count
  3   2
  5   3
  </code></pre>
  
  <p>Count : how many times that A exist in B</p>