问题与自我有一个子查询加盟;想知道2个查询下面

Question

该工作的区别：

SELECT a.year, a.name, a.runs 
from players a JOIN 
    (SELECT year, max(runs) runs FROM players GROUP BY year 
    ) b 
    ON (a.year = b.year AND a.runs = b.runs); 

这不是工作：

select a.name,b.year,b.run 
from players a join 
    (select year, max(runs) as run, name from players group by year 
    ) b 
    on a.year = b.year AND a.runs = b.run; 

有人可以plz帮助我理解这一点？

Answer 1

第二加入查询不正确组由

 (select year, max(runs) as run, name from players group by year 
) b 

，因为你选择也name应该按

 (select year, max(runs) as run, name from players group by year, name 
) b 

但是这会给你不同的结果