利用延迟关联或者子查询优化超多分页场景
EXPLAIN SELECT * FROM `demo` limit 300000,20

EXPLAIN SELECT a.* FROM demo a, (select id from demo LIMIT 300000,20 ) b where a.id=b.id

EXPLAIN SELECT * FROM `demo` limit 300000,20

EXPLAIN SELECT a.* FROM demo a, (select id from demo LIMIT 300000,20 ) b where a.id=b.id
