Question

这是我第一次尝试使用JOIN MySQL语句......

我有2张表.. games和games_ratings

两个表都有一个id列。 id代表游戏的id。而我只想得到评级栏中的平均值，其中games_ratings中的id等于游戏表中的id。

SELECT a.id, a.name, AVG(b.rating) AS average FROM games a LEFT JOIN games_ratings b GROUP BY a.id ORDER BY average DESC LIMIT 50;

任何想法？

Answer 1

试试这个：

SELECT a.id, a.name, AVG(b.rating) AS average 
    FROM games a 
    LEFT JOIN games_ratings b
    ON a.id = b.id # <-- You need this line I believe 
GROUP BY a.id
ORDER BY average DESC LIMIT 50;

编辑：如果没有完整的架构，这有点难，但您可以尝试这样的事情。

SELECT a.id, a.name, AVG(b.rating) AS average, COUNT( b.id) as votes
    FROM games a 
    LEFT JOIN games_ratings b
    ON a.id = b.id 
GROUP BY a.id
ORDER BY votes DESC, average DESC LIMIT 50; # <-- You may need to modify this line

Answer 2

不要忘记他要求的WHERE条款：

其中games_ratings中的id等于游戏表中的id

> SELECT a.id, a.name, AVG(b.rating) AS average 
>     FROM games a 
>     LEFT JOIN games_ratings b
>     ON a.id = b.id # <-- You need this line I believe
>     **WHERE a.id = b.id**  
>     GROUP BY a.id 
>     ORDER BY average DESC LIMIT 50;

如何在JOIN语句中指定WHERE？

2 个答案: