Faster SQL search with Union operation in Ruby on Rails

application_record.rb

class ApplicationRecord
  # ...
  scope :union, ->(*others) { from_unions(self, *others) }

  def self.from_unions(*relations)
    subquery = relations.map(&:arel).inject(:union)
    unscoped.from subquery.as(table_name)
  end
  # ...
end

author.rb

class Author < ApplicationRecord
  has_many :books

  scope :matching_name, ->(q) { where(table[:name].matches("%#{q}%")) }
end

new_book.rb

class Book < ApplicationRecord
  # ...
  scope :search, ->(q) {
    where(ean: q).union(
      matching_title(q),
      matching_description(q),
      matching_author(q)
    )
  }
  # ...
end

old_book.rb

class Book < ApplicationRecord
  belongs_to :author
  
  scope :old_search, ->(q) {
    where(ean: q)
      .or matching_title(q)
      .or matching_description(q)
      .or matching_author(q)
  }

  scope :matching_title, ->(q) { where(table[:title].matches("%#{q}%")) }
  scope :matching_description, ->(q) { where(table[:description].matches("%#{q}%")) }
  scope :matching_author, ->(q) { left_joins(:author).merge(Author.matching_name(q)) }
end