Examples:<br><br>InnoDB : 50% slower.<br>MyISAM: 6X slower.<br><br>Conclusions:<br><ol><li> CHAR keys are indeed slower for joins compared to integer keys </li><li> Performance degradation can range from few percent to couple of times  for Innodb tables
</li><li> MyISAM Tables may suffer significantly if key compression is not disabled </li><li> Joining on Shorter CHAR keys is significantly faster than Long keys </li><li> Latin1 (I guess any simple encoding) is significantly faster for joins compared to UTF8 
</li></ol>Details here<br><br><a href="http://www.mysqlperformanceblog.com/2007/06/18/using-char-keys-for-joins-how-much-is-the-overhead/">http://www.mysqlperformanceblog.com/2007/06/18/using-char-keys-for-joins-how-much-is-the-overhead/
</a><br clear="all"><br>