SQL 其中连接集必须包含所有值但可能包含更多

Question

我有三个表 offers、sports 和连接表 offers_sports。

class Offer < ActiveRecord::Base
  has_and_belongs_to_many :sports
end

class Sport < ActiveRecord::Base
  has_and_belongs_to_many :offers
end

我想选择包含一组给定运动名称的优惠。它们必须包含所有运动，但可以包含更多。

假设我有这三个优惠:

light:
  - "Yoga"
  - "Bodyboarding"
medium:
  - "Yoga"
  - "Bodyboarding"
  - "Surfing"
all:
  - "Yoga"
  - "Bodyboarding"
  - "Surfing"
  - "Parasailing"
  - "Skydiving"

给定数组 ["Bodyboarding", "Surfing"] 我想得到 medium 和 all 但不是 light 。

我尝试了类似 this answer 的方法但我在结果中得到零行:

Offer.joins(:sports)
     .where(sports: { name: ["Bodyboarding", "Surfing"] })
     .group("sports.name")
     .having("COUNT(distinct sports.name) = 2")

转换为 SQL:

SELECT "offers".* 
FROM "offers" 
INNER JOIN "offers_sports" ON "offers_sports"."offer_id" = "offers"."id"     
INNER JOIN "sports" ON "sports"."id" = "offers_sports"."sport_id" 
  WHERE "sports"."name" IN ('Bodyboarding', 'Surfing') 
GROUP BY sports.name 
HAVING COUNT(distinct sports.name) = 2;

ActiveRecord 答案会很好，但我会满足于只使用 SQL，最好是与 Postgres 兼容。

数据:

offers
======================
id | name
----------------------
1  | light
2  | medium
3  | all
4  | extreme

sports
======================
id | name
----------------------
1  | "Yoga"
2  | "Bodyboarding"
3  | "Surfing"
4  | "Parasailing"
5  | "Skydiving"

offers_sports
======================
offer_id | sport_id
----------------------
1        | 1
1        | 2
2        | 1
2        | 2
2        | 3
3        | 1
3        | 2
3        | 3
3        | 4
3        | 5
4        | 3
4        | 4
4        | 5

Answer 1

按 offer.id 分组，而不是按 sports.name(或 sports.id)分组:

SELECT o.*
FROM   sports        s
JOIN   offers_sports os ON os.sport_id = s.id
JOIN   offers        o  ON os.offer_id = o.id
WHERE  s.name IN ('Bodyboarding', 'Surfing') 
GROUP  BY o.id  -- !!
HAVING count(*) = 2;

假设典型的实现:

• offer.id 和 sports.id 定义为主键。
• sports.name 被定义为唯一的。
• (sport_id, offer_id) 在 offers_sports 中定义为唯一(或 PK)。

计数中不需要 DISTINCT。而且 count(*) 甚至更便宜一些。

包含一系列可能技术的相关答案:

• How to filter SQL results in a has-many-through relation

---

由@max(OP)添加 - 这是将上述查询整合到 ActiveRecord 中:

class Offer < ActiveRecord::Base
  has_and_belongs_to_many :sports
  def self.includes_sports(*sport_names)
    joins(:sports)
      .where(sports: { name: sport_names })
      .group('offers.id')
      .having("count(*) = ?", sport_names.size)
  end
end