title: INDEX on DATE field and MONTH() YEAR() functions
body: <p>Is it still correct than an index on a date/datetime column is not optimized for YEAR(col), MONTH(col) functions?  Bill Karwin gave a pretty definitive answer <a href="http://forums.mysql.com/read.php?115,86654,86654#msg-86654" rel="noreferrer">here</a>, but since this was from ten years ago I wanted to check.  I would have thought that since the date column is described as </p>
  
  <blockquote>
    <p>A three-byte integer packed as YYYY×16×32 + MM×32 + DD</p>
  </blockquote>
  
  <p>that it could be indexed in such a way that it could be optimized in the same way that multi column indexes are when a <a href="http://dev.mysql.com/doc/refman/5.7/en/group-by-optimization.html" rel="noreferrer">tight index scan</a> is performed.</p>
  
  <p>Is it true this optimization still does not exist?  And why wouldn't it be possible?</p>