某php里面，sql如下
select count(*) from a, (select sum(b) as b from c where c.id=a.id ) as d whee a.id= b.aid and a.xxxx = ??? and a.yyyy=?????
用来做分页的满足条件记录数量的统计，看上去不错。
但我们考虑如下场景，当 a里面满足 a.xxxx = ??? and a.yyyy=????? 的记录达到万条，那么 (select sum(b) as b from c where c.id=a.id )
不也要计算万次?
优化方法如下:
删除(select sum(b) as b from c where c.id=a.id )
而在每个分页展示的时候，发出 rowcountperpage 个统计。
将大大减轻查询负载。