如何优化MySQL ORDER BY +巨大的LIMIT偏移量

Question

表:

CREATE TABLE `test` (
  `uid` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `rating` smallint(5) unsigned NOT NULL DEFAULT '100',
  PRIMARY KEY (`uid`),
  KEY `rating` (`rating`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

此查询运行得足够快(0.015秒):

SELECT uid FROM test ORDER BY rating DESC LIMIT 0,100

但是有很大的LIMIT偏移它运行得很慢(2.215s):

SELECT uid FROM test ORDER BY rating DESC LIMIT 10000,100

怎么能摆脱巨大的LIMIT抵消？!

Answer 1

用LIMIT 10000, 100MySQL必须扫描10100条记录.如果你能记住你在窗口中的位置,那可能会更好:

SELECT uid
FROM test
WHERE rating > :last_rating
ORDER BY rating DESC LIMIT 0,100

在这种情况下:last_rating是上一个查询的最后一个评级.