SQL where 连接集必须包含所有值，但可以包含更多值

我有三张桌子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

我想选择的优惠include给定的运动名称数组。他们must包含所有的sports but may有更多的。

假设我有这三个报价：

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

给定数组["Bodyboarding", "Surfing"]我想要得到medium and all但不是light.

我尝试过类似的事情这个答案 https://stackoverflow.com/a/23721658/544825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")

翻译成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，但我会选择 SQL，最好是与 Postgres 兼容。

Data:

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

通过...分组offer.id，不是由sports.name (or sports.id):

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 and sports.id被定义为主键。
• sports.name被定义为唯一的。
• (sport_id, offer_id) in offers_sports被定义为唯一的（或 PK）。

你不需要DISTINCT在计数中。和count(*)甚至还便宜一点。

相关答案与一系列可能的技术：

• 如何在多通关系中过滤 SQL 结果 https://stackoverflow.com/questions/7364969/how-to-filter-sql-results-in-a-has-many-through-relation/7774879#7774879

由@max（OP）添加 - 这是上面的查询被滚动到 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