Examples: InnoDB : 50% slower. MyISAM: 6X slower. Conclusions: 1. CHAR keys are indeed slower for joins compared to integer keys 2. Performance degradation can range from few percent to couple of times for Innodb tables 3. MyISAM Tables may suffer significantly if key compression is not disabled 4. Joining on Shorter CHAR keys is significantly faster than Long keys 5. Latin1 (I guess any simple encoding) is significantly faster for joins compared to UTF8 Details here http://www.mysqlperformanceblog.com/2007/06/18/using-char-keys-for-joins-how...