mysql执行顺序问题

疑惑求解：sql的执行顺序是 from > where > group by > select > order by > limit，这条语句里面group by day 应该是错误的，因为 day 这个别名还没有被执行，select在group by 后面执行。但是我这条语句自测运行通过了，我很不解。
有人可以解答我这个问题吗？

select day(date) as day , count(question_id) as question_cnt
from question_practice_detail
where year(date) = "2021" and month(date) = "08"
group by day;

你把别名day换一个试试。比如myday

这篇文章讲的很详细，请看：MySQL执行存储过程