title: Efficiency UPDATE WHERE ... vs CASE ... WHEN
body: <p>In the case of a big table (~5 millions lines) what is more efficient to update all lines that matches a condition (circa 1000 rows): </p>
  
  <p><strong>1.</strong> A simple update statement ? </p>
  
  <pre><code>UPDATE table SET last_modif_date = NOW() WHERE condition; 
  </code></pre>
  
  <p><strong>2.</strong> A case when that perform an update if condition matches </p>
  
  <pre><code>UPDATE table SET
  last_modif_date = (CASE WHEN CONDITION THEN NOW() ELSE last_modif_date END)
  </code></pre>
  
  <p>And why ?</p>
  
  <p>Thanks in advance</p>