Ruby中的优化（快速）ActiveRecord等价物是什么：

SELECT DISTINCT customers.city 
FROM customers
INNER JOIN (
  SELECT c_id 
  FROM carts
  WHERE shop_id = #{`shop_id`}
  ORDER BY created_at DESC 
  LIMIT 1000 OFFSET 1000
) AS filtered_carts ON customers.id = filtered_carts.c_id;

注意：shop_id是传递给查询/关联的ruby变量。谢谢
上面的SQL运行得和预期的一样快。
我试图找到一个纯粹的ActiveRecord解决方案来避免类似这样的事情：

customers = Customer
  .select(:city)
  .distinct
  .joins("
    INNER JOIN (
      SELECT c_id
      FROM carts
      WHERE shop_id = #{`shop_id`}
      ORDER BY created_at DESC
      LIMIT 1000 OFFSET 1000
    ) AS filtered_carts
    ON customers.id = filtered_carts.c_id
  ")

原因是为了避免在ActiveRecord中硬编码SQL，以防止未来可能出现的最终模型更改和迁移的向后兼容性问题。