How to aggregate alias column in activerecord?

To aggregate an alias column in ActiveRecord, you can use the select method along with the group method. First, you create the alias column using SQL's AS keyword in the select clause, and then you use the group method to perform the aggregation based on that alias column.

Let's assume you have a model named Product with a price column, and you want to find the total price of products for each category and display it as an alias column called total_price.

Here's how you can achieve this using ActiveRecord:

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class Product < ApplicationRecord
  belongs_to :category
end

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# In your controller or wherever you want to perform the aggregation
def aggregate_by_category
  # Use the select method to create the alias column `total_price`
  # and perform the aggregation with the SUM function
  products_by_category = Product.select("category_id, SUM(price) AS total_price")
                               .group(:category_id)

  # Access the alias column `total_price` using the getter method
  products_by_category.each do |product|
    puts "Category ID: #{product.category_id}, Total Price: #{product.total_price}"
  end
end

In the example above, the select method creates the alias column total_price using the SQL AS keyword and calculates the sum of the price column using the SUM function. The group method groups the results by the category_id.

When you iterate through the products_by_category collection, you can access the total_price value using the getter method product.total_price.

This will generate a SQL query that looks something like:

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SELECT category_id, SUM(price) AS total_price
FROM products
GROUP BY category_id

The result will be a collection of objects with the category_id and total_price attributes representing the aggregated data for each category.