优化mysql分页排序查询的办法

很简单的100w条数据用 select id from guestbook order by id desc limit 190000,30 查询起来，页面不动弹了。

后来请教了高人，换了下面的语句

SELECT * FROM guestbook INNER JOIN (select id from guestbook order by id desc limit 190000,30 )as d ON guestbook .id=d.id order by guestbook .id desc limit 30

结果2s结果就出来了，太神奇了。

研究了一下这个语句还可以简写为

SELECT * FROM guestbook INNER JOIN (select id from guestbook order by id desc limit 190000,30 )as d ON guestbook .id=d.id

关键问题就在两个sql语句之间的差别

select　＊　 from guestbook order by id desc limit 190000,30  //这个会很慢

 select id from guestbook order by id desc limit 190000,30 //这个可能是加了索引，比较快，而且只查了id字段，然后把查询的结果再做个内连接就得到需要的数据了