title: Get SUM of COUNTs for several tables
body: <p>OK, so here's what I need :</p>
  
  <p>Let's say we've got a table, e.g. <code>A</code> and need to get the number of rows.</p>
  
  <p>In that case we'd <code>SELECT COUNT(*) FROM A</code>.</p>
  
  <p>Now, what if we have 3 different tables, let's say <code>A</code>, <code>B</code> and <code>C</code>.</p>
  
  <p>How can I get the total number of rows in all three of them?</p>