Question

实体之间的OneToMany关系：

Composer＆gt; Soundtrack
Soundtrack＆gt; SoundtrackRating

我希望按给定的Soundtrack选择每个Composer，并为每个SoundtrackRatings支付Soundtrack的费用。

在DQL：

SELECT s.name, (SUM(r.rating)/COUNT(r.rating)) AS rating 
FROM Soundtrack AS s 
LEFT JOIN SoundtrackRating AS r 
WHERE s.composer = :composer AND r.soundtrackId = s.id 
GROUP BY s.id 
ORDER BY rating DESC

然后我传递:composer类型Composer的实例：

$em->createQuery($dql)
  ->setParameter('composer', $composer)
  ->getResult();

然而，在查询结果中，无论Soundtrack我作为参数传递，我都会收到所有$composer个条目。唯一的区别是只能平均给定$composer的评分，其余的平均值为0。

此查询中的问题在哪里？

Answer 1

想出来。从r.soundtrackId = s.id子句中移除WHERE并使用WITH中的LEFT JOIN代替：

SELECT s.name, (SUM(r.rating)/COUNT(r.rating)) AS rating 
FROM Soundtrack AS s 
LEFT JOIN SoundtrackRating AS r WITH r.soundtrackId = s.id
WHERE s.composer = :composer 
GROUP BY s.id 
ORDER BY rating DESC

DQL OneToMany查询和执行平均值

1 个答案: