求助，请告诉我这个查询语句的执行过程

select filmname,rating,price,c1.cc from
movie as m1 inner join cc as c1 on c1.cid=m1.cid
where m1.price =
    (select MIn(price) from movie as m2
    where m1.cid=m2.cid
    and m2.rating=
        (select max(m3.rating) from movie as m3
        where m3.cid=m2.cid
        group by m3.cid)
    group by m2.cid)
我不理解的地方就是这里的子查询返回的值是多个（我想这个大家可以想象的），为什么可以直接用“=”？