SQL wherejoined set 必须包含所有值，但可以包含更多 [英] SQL where joined set must contain all values but may contain more

问题描述

我有三个表offers、sports和连接表offers_sports.

I have three tables offers, sports and the join table offers_sports.

class Offer < ActiveRecord::Base
  has_and_belongs_to_many :sports
end

class Sport < ActiveRecord::Base
  has_and_belongs_to_many :offers
end

我想选择包括一系列给定的运动名称的优惠.它们必须包含所有sports，但可能有更多.

I want to select offers that include a given array of sport names. They must contain all of the sports but may have more.

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"] 我想要 medium 和 all 但不是 light.

Given the array ["Bodyboarding", "Surfing"] I would want to get medium and all but not light.

我已经尝试了类似这个答案的方法，但结果中的行数为零:

I have tried something along the lines of this answer but I get zero rows in the result:

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 的答案会很好，但我只会满足于 SQL，最好与 Postgres 兼容.

An ActiveRecord answer would be nice but I'll settle for just SQL, preferably Postgres compatible.

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

推荐答案

Group by offer.id，而不是 sports.name(或 sports.id):

Group by offer.id, not by 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;

假设典型实现:

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

• offer.id and sports.id are defined as primary key.
• sports.name is defined unique.
• (sport_id, offer_id) in offers_sports is defined unique (or PK).

计数中不需要 DISTINCT.而且 count(*) 甚至更便宜一些.

You don't need DISTINCT in the count. And count(*) is even a bit cheaper, yet.

与一系列可能的技术相关的答案:

Related answer with an arsenal of possible techniques:

• 如何过滤SQL 导致具有多通关系

由@max(OP)添加 - 这是上面的查询滚动到 ActiveRecord 中:

Added by @max (the OP) - this is the above query rolled into ActiveRecord:

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

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