选择带有分组依据的小写字母列，或在Rails 4中选择小写（列） [英] Select lower case column with group by or select lower(column) in Rails 4

问题描述

如何在Rails 4中实现跟踪？

How to achieve following in rails 4?

这是我的PostgreSQL查询，可以正常工作

Here is my PostgreSQL query and works correctly

SELECT lower(name) as c_name, count(*) as cc FROM categories  GROUP BY c_name  ORDER BY cc desc LIMIT 3

ii给了我以下结果

 "ecommerce solutions";6
 "vmware";6
 "big data analytics";5

但是当我在Rails 4中编写与

But when I write same query in Rails 4 as

Category.select("lower(name) as c_name, count(*) as cc").group("c_name").order("cc desc").limit(3) 

以上查询生成与上面的PostgreSQL查询相同的以下查询

Above query generates following query which is same as above PostgreSQL query

SELECT lower(name) as c_name, count(*) as cc FROM "categories"  GROUP BY c_name  ORDER BY cc desc LIMIT 3

给出以下结果

[#<Category id: nil>, #<Category id: nil>, #<Category id: nil>]

为什么会这样？当我将查询切到

Why this is happening ? when I cut my query to

 Category.select("lower(name)").limit(3)

这也不起作用，结果变成

This also does not work, and results into

 [#<Category id: nil>, #<Category id: nil>, #<Category id: nil>]

我想在 lower（name）上分组，计数为聚合，我有很多<$ 类别模型

I want to do group on lower(name) with count as aggregation, I have many variances of name in Category model

Ex中的c $ c>名称。数据集

Ex. data set

"Vmware" and "VMware" and "VMWARE" and "vmware" 

我如何在Rails 4中对lower（name）进行分组？

How can I group on lower(name) in Rails 4?

用简单的话说，如何在Rails 4中编写以下等效查询？

In simple words, How to write equivalent query of following in Rails 4?

SELECT lower(name) as c_name, count(*) as cc FROM categories  GROUP BY c_name  ORDER BY cc desc LIMIT 3

推荐答案

结果正确，但Rails显示错误。只需手动访问结果即可：

The result is correct, but Rails displays it wrong. Just access results manually:

results = Category.select("lower(name) as c_name, count(*) as cc").group("c_name").order("cc desc").limit(3) 
results.first['c_name']

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