title: Terser syntax for ON DUPLICATE KEY UPDATE only if one condition is true?
body: <p>I know I can do something like </p>
  
  <pre><code>ON DUPLICATE KEY UPDATE 
      exampleColumn1 = IF (exampleCondition = 1, VALUES(exampleColumn1), exampleColumn1),
      exampleColumn2 = IF (exampleCondition = 1, VALUES(exampleColumn2), exampleColumn2),
      exampleColumn3 = IF (exampleCondition = 1, VALUES(exampleColumn3), exampleColumn3),
      # Etc etc
  </code></pre>
  
  <p>But since I'm doing the exact same condition check every time, surely there's a terser way to write this?  It would be especially nice in those cases where the condition is a bit longer to write out.  </p>
  
  <p>From what I've read, it seems possible if I wrote a function for this, but can I do it in a plain old query?</p>