title: Update query to copy one column data to another fails
body: <p>Following query gives error 1064. Why?</p>
  
  <pre><code>update projects 
  set project_renewal = select project_renewal from Project_number;
  </code></pre>
  
  <p>I tried this</p>
  
  <pre><code>update projects 
  set project_renewal = (select project_renewal from Project_number)
  </code></pre>
  
  <p>Then it gives error 1242. Subquery returns more than one row.</p>