ORDER BY Optimization

http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html

SELECT * FROM t1
ORDER BY_`key_part1`_,_`key_part2`_,... ;

SELECT * FROM t1
WHERE_`key_part1`_=_`constant`_
ORDER BY_`key_part2`_;

SELECT * FROM t1
ORDER BY_`key_part1`_DESC,_`key_part2`_DESC;

SELECT * FROM t1
WHERE_`key_part1`_=1
ORDER BY_`key_part1`_DESC,_`key_part2`_DESC;