原博文地址：https://blog.csdn.net/baidu_38083619/article/details/82463058
总结：pageHelper是通过limit拼接sql实现分页的
低效率查询语句：select * from user where age = 10 limit 100000,10；
高效率查询语句：
SELECT a.* FROM USER a
INNER JOIN
(SELECT id FROM USER WHERE age = 10 LIMIT 100000,10) b
ON a.id = b.id;