title: Selecting distinct values from two tables
body: <p>I have two rather large databases (+1 million rows each).  Both tables have the same structure.</p>
  
  <p>How can I check if each value in a column is unique across both tables?</p>
  
  <p>Is there a<br>
  <code>SELECT COUNT(DISTINCT</code>col<code>) FROM tbl</code><br>
  type of query that will consider BOTH tables?</p>
  
  <p>Thanks!</p>