通过子查询或连接Hive sql avg表

Question

我有两张桌子：

影

movieid int                                         
title   string  

评分

userid    int                                       
movieid   int                                       
rating    float                                     
timestamp string 

我想得到像这样的结果

movietitle ratingavg
--------------------   
movie 1     4.8
movie 2      8

这是我的疑问：

select avg(r.rating), m.title 
from ratings r 
join movies m on r.movieId = m.movieId;

和这个

select m.title, (select avg(r.rating) from ratings r) 
from movies m 
join ratings r on r.movieId = m.movieId;

但是我收到了一个错误：

  

失败：SemanticException [错误10025]：行1:21表达式不在GROUP BY键'title'

Answer 1

SELECT avg(r.rating)
    ,m.title
FROM ratings r
JOIN movies m ON r.movieId = m.movieId
GROUP BY m.title;