Express SQL UNION 查询 Rails 方式

使用Express和SQL UNION查询是Rails中常见的一种查询方式。通过使用这种方式，可以将两个或多个查询的结果合并成一个结果集。在本文中，将介绍如何在Rails中使用SQL UNION查询，并提供一个实际案例代码。

ruby
class User < ApplicationRecord
  def self.union_query
    sql = "(SELECT id, name FROM users WHERE age < 30) UNION (SELECT id, name FROM users WHERE age > 50)"
    find_by_sql(sql)
  end
end

ruby
class User < ApplicationRecord
  def self.find_users_by_conditions(conditions)
    queries = conditions.map { |condition| "SELECT id, name FROM users WHERE #{condition}" }
    sql = queries.join(" UNION ")
    find_by_sql(sql)
  end
end

ruby
class UsersController < ApplicationController
  def index
    conditions = ["age < 30", "age > 50", "gender = 'female'"]
    @users = User.find_users_by_conditions(conditions)
  end
end

ruby
<% @users.each do |user| %>
  
<%= user.name %>
<% end %>