佳音的博客

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;