Specify which Index to use during a SELECT

MySQL by default will always use the best index for a SELECT. MySQL is not perfect and at times will mess this up by using a wrong index. In such cases you can force MySQL to use a specific index or otherwise ask it to ignore a specific index.

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;