title: create table with select union has no constraints
body: <p>I created a table using <code>select</code> with a <code>union</code>, as follows:</p>
  
  <pre><code>create table tableC as
  select column1, column2 from tableA
  union all
  select column1, column2 from tableB
  </code></pre>
  
  <p>The resulting table (<code>tableC</code>) has inherited none of the constraints from <code>tableA</code> or <code>tableB</code>. Why weren't the constraints copied to the new table?</p>