Question

该查询工作正常，但作为一个练习，我将如何转换它利用ActiveRecord方法？

Model.find_by_sql("SELECT *, SUM(impressions) AS impressions, SUM(cost) AS cost 
        FROM display_stats 
        WHERE (created_at >= '#{(Date.today-2).to_time.strftime('%Y-%m-%d')}' 
          AND created_at <= '#{(Date.today-1).to_time.strftime('%Y-%m-%d')}') 
        GROUP BY banner_id 
        ORDER BY cost DESC") 

这里是我的模型结构：

DisplayStat (id: integer, 
      banner_id: integer, 
      comments: string, 
      impressions: integer, 
      cost: integer, 
      created_at: datetime, 
      updated_at: datetime) 

是否可以写上面的查询，而无需使用原始的SQL？

---

的运转轨道3.1和MySQL 5.5

Answer 1

试试这个：

DisplayStat. 
    select("banner_id, SUM(impressions) AS impressions, SUM(cost) AS cost"). 
    where(:created_at => (2.days.ago.beginning_of_day..2.days.ago.end_of_day)). 
    group(:banner_id). 
    order("cost DESC") 

的日期范围是从开始到一天结束的时候; 2天前。当您将日期范围传递给条件散列时，rails会生成一个BETWEEN运算符。