ActiveRecord从组中获取平均值

我正在尝试在ActiveRecord 4中编写此查询，但无济于事。ActiveRecord从组中获取平均值

SELECT date, AVG(gain) AS avg_gain FROM counters WHERE (date > '2014-03-03' ) GROUP BY date ORDER BY date DESC;

所以我炒了一起：

Counter.select("date, AVG(gain) as avg_gain").where("date > '2014-03-03'").group(:date).order(date: :desc) 
=> #<ActiveRecord::Relation [#<Counter id: nil, date: "2014-04-01">, #<Counter id: nil, date: "2014-03-31">, #<Counter id: nil, date: "2014-03-30">, #<Counter id: nil, date: "2014-03-29">, #<Counter id: nil, date: "2014-03-28">, #<Counter id: nil, date: "2014-03-27">, #<Counter id: nil, date: "2014-03-26">, #<Counter id: nil, date: "2014-03-25">, #<Counter id: nil, date: "2014-03-24">, #<Counter id: nil, date: "2014-03-23">, ...]>

唯一的麻烦是，该结果不包含avg_gain列。有任何想法吗？

来源

2014-04-01 if __name__ is None

当您使用select时，所选字段将添加到返回的关系中的实例。返回的结果不包括打印输出中的所选字段。

访问这些字段，就像你访问一个列的属性：

result = Counter.select("date, AVG(gain) as avg_gain").where("date > '2014-03-03'").group(:date).order(date: :desc) 
result.first.avg_gain # Prints expected value for the first Counter

来源

2014-04-01 18:46:23 vee

有什么办法，我可以掐出来？像'Counter.select（“date，AVG（gain）as avg_gain”）。其中（“date>'2014-03-03'”）。group（：date）.order（date：：desc）.pluck（：日期，“avg_gain”）'？ –

@JanNetherdrake你可以做'result.map {| counter | [counter [：date]，counter [：avg_gain]]}'返回像[[[date，avg]，[date，avg]，...] – MrYoshiji

ActiveRecord从组中获取平均值

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