SQL的问题 关于max函数的使用

select yr ,count(title) from movie
join casting on (casting.movieid=movie.id)
join actor on (casting.actorid=actor.id)
where actor.name='John Travolta'
group by yr

```having count(title) =(
select max(count(title)) from
 (select yr,count(title) from movie
join casting on (movieid=movie.id)
join actor on (actorid=actor.id)
where name='John Travolta'
group by yr) as T
)

SELECT yr ,count(title) FROM movie
JOIN casting oN movieid=movie.id
join actor on actorid=actor.id
where actor.name='John Travolta'
group by yr

```having count(title) =(
select max(c) from
 (select yr,count(title) as c from movie
join casting on movie.id=movieid
join actor on actorid=actor.id
where name='John Travolta'
group by yr) as T
)

两种情况差异在于二次筛选的时候，查询最大值的时候，一个有别名，一个没有
答案为什么会有差异