一条SQL的运行顺序

客户端 -> 链接模块 -> 解析器 -> 优化器(执行计划) -> 执行器 -> InnoDB

一条SQL查询语句的执行顺序

编写顺序:
select -> from -> where -> group by -> having -> order by -> limit
运行顺序:
from -> where -> group by -> having -> select -> order by -> limit