如何在AREL中对分组列求和 [英] How to sum a grouped column in AREL

问题描述

在 Rails 3/AREL 中

in Rails 3/AREL

Model.group(:label).sum(:value) 会做

SELECT sum(value), label from model_table group by label

我正在努力寻找 AREL 的做法

I am trying to find the AREL way of doing

SELECT sum(value) from (select value, label from model_table group by label)

这是 Model.group(:label).map(&:value).sum 使用 ruby​​ 求和，我如何在 SQL/AREL 中执行此操作

which is Model.group(:label).map(&:value).sum using ruby to sum, how do I do this in SQL/AREL

推荐答案

不确定这是否有意义.您的核心 SQL 无效:

Not sure this makes sense. Your core SQL is not valid:

SELECT value, label FROM model_table GROUP BY label

如果您的选择中没有聚合函数(例如 SUM)，则无法使用 GROUP BY.我想你真正想要的是这个:

You cannot have a GROUP BY without an aggregation function (e.g. SUM) in your select. I think what you actually want is this:

SELECT label, SUM(value) from model_table GROUP BY label

我说得对吗?要在 AREL 中执行此操作，请尝试以下操作:

Am I right? To do this in AREL, try this:

relation = Model.select(:label).
  select(Model.arel_table[:value].sum.as("value_sum")).
  group(:label)
relation.to_sql
# => SELECT label, SUM("model_table"."impressions") AS value_sum FROM "model_table" GROUP BY label 

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