mysql - 如何使用 ActiveRecord 进行多项计算

Question

我有一个简单的国家表，其中包含名称、大陆、人口和其他一些字段。

我正在尝试使用 ActiveRecord 执行以下 MySQL 查询

SELECT count(*), SUM(population), AVG(population) FROM countries wherecontinent='Asia'

我应该怎么做？

我试过了：

Country.where(:continent => 'Asia').count()

Country.where(:continent => 'Asia').sum(:population)

Country.where(:continent => 'Asia').average(:population)

所有单独工作都很好，它们都返回数字（不是 ActiveRelation 对象），这意味着你不能做类似的事情

Country.where(:continent => 'Asia').count().sum(:population).average(:population)

Answer 1

找到了解决方案：

结果 = Country.select("count(*) as num_countries, sum(population) as total_population, avg(population) as average_population).where(:continent => 'asia').to_a[0]

然后，您可以像这样访问结果：result.num_countries、result.total_population 和 result.average_population

Answer 2

你可以试试：

ActiveRecord::base.connection.execute('SELECT count(*), SUM(population), AVG(population) FROM countries where continent='Asia')

这将返回一个哈希：

{'count(*)': count, ... }