HINT

 

SELECT * FROM table1 USE INDEX (col1_index,col2_index)
  WHERE col1=1 AND col2=2 AND col3=3;

SELECT * FROM table1 IGNORE INDEX (col3_index)
  WHERE col1=1 AND col2=2 AND col3=3;

1、http://dev.mysql.com/doc/refman/5.5/en/index-hints.html

2、https://en.wikipedia.org/wiki/Hint_(SQL)