优化思路

减少表之间的关联

处理示例：

数据量：4877080

-- 算法1 --
select 
sum(if(`name`="张三",age,0))
,sum(if(`name`="李四",age,0))
from test1
where `name` in ("张三","李四");
-- 计算时间 2.227s
-- 算法2 --
select 
sum(a.age)
,sum(b.age)
from test1 a left join test1 b on  a.id+1 = b.id
where a.`name` = "张三";
-- 时间: 73.465s