WL#556: Automatic disabling of duplicated keys:

Automaticly disabling all keys for which there is a shorter key over
the same columns that can be used and no one of the extra key parts are
used.

(Can be done in 'sql_select.cc::update_ref_and_keys()')

Example:

CREATE TABLE t1 (
  FieldKey varchar(36) NOT NULL default '',
  LongVal bigint(20) default NULL,
  StringVal mediumtext,
  KEY FieldKey (FieldKey),
  KEY LongField (FieldKey,LongVal),
  KEY StringField (FieldKey,StringVal(32))
);

SELECT * FROM t1 where t1.FieldKey = 'edf162e0-f712-11d6-af6b-c8c40a0a1096';

In this case we should disable LongField and StringField (for this query) 
as these are not useful here.