GroupingError：ERROR：列必须出现在GROUP BY子句中或用于聚合函数

I have code in my controller that is ranking albums by the highest average review rating (used code from this solution How to display highest rated albums through a has_many reviews relationship):

我的控制器中的代码是按最高平均评价等级排名的专辑（此解决方案中使用的代码如何通过has_many评论关系显示评分最高的专辑）：

@albums = Album.joins(:reviews).select("*, avg(reviews.rating) as average_rating").group("albums.id").order("average_rating DESC")

This code works perfectly in my development environment (sqlite3), however when I pushed the code to heroku and to postgresql I got this error:

这段代码在我的开发环境（sqlite3）中运行得很好，但是当我将代码推送到heroku和postgresql时，我遇到了这个错误：

PG::GroupingError: ERROR:  column "reviews.id" must appear in the GROUP BY clause or be used in an aggregate function

I realize this is a fairly common problem, I am a bit inexperienced with SQL so I am having trouble refactoring the code so it will work in both my development and production environments.

我意识到这是一个相当普遍的问题，我对SQL有点缺乏经验，所以我在重构代码时遇到了麻烦，因此它可以在我的开发和生产环境中工作。

3 个解决方案

#1

You are not allowed to select reviews.id (selected implicitly through the wildcard *) without adding it to the GROUP BY clause or applying an aggregate function like avg(). The solution is to do one of the following:

您不能选择reviews.id（通过通配符*隐式选择），而不将其添加到GROUP BY子句或应用像avg（）这样的聚合函数。解决方案是执行以下操作之一：

Remove the wildcard * from your select
从您的选择中删除通配符*
Add the field reviews.id to your group clause
将字段reviews.id添加到您的组子句中
Select reviews.id explicitly and apply an aggregate function to it (e.g. sum(reviews.id))
明确选择reviews.id并对其应用聚合函数（例如sum（reviews.id））
Replace the wildcard * with the table-specific wildcard albums.*
将通配符*替换为特定于表的通配符相册。*

The second and third option do not make much sense in your scenario though. Based on your comment, I added option four.

第二个和第三个选项在你的场景中没有多大意义。根据您的评论，我添加了选项四。

#2

Just would like to share this code on ruby using active record (sinatra)

只是想使用活动记录（sinatra）在ruby上分享这段代码

I had to add "group by" to an "order by" function, so line of code ...

我不得不将“group by”添加到“order by”函数中，因此代码行...

from:

从：

@models = Port.all.order('number asc')

to:

至：

@models = Port.select(:id, :device_id, :number, :value, :sensor, :UOM).all.order('number asc').group(:id,:sensor,:UOM)

and it worked perfect, just remember the ID field in this case "Port.id" must be added to the group clause otherwise will raise this error, and as @slash mentioned you can not achieve this with special functions (select implicitly through the wildcard * or in my case using "all")

并且它工作得很完美，只需记住ID字段在这种情况下“Port.id”必须添加到group子句中否则会引发此错误，并且正如@slash所提到的那样你无法通过特殊函数实现这一点（通过通配符隐式选择） *或在我的情况下使用“全部”）

#3

The only really acceptable solution I found to this kind of problem was with this code:

我发现这种问题的唯一真正可接受的解决方案是使用以下代码：

@albums = Album.joins(:reviews).select("*, avg(reviews.rating) as average_rating").group_by(&:id).order("average_rating DESC")

I hope it helps someone.

我希望它对某人有帮助。

#1