SQL - 计算兴趣之间的重叠

Question

我有一个如下所示的架构（具有适当索引的数百万条记录）：

groups    |  interests
------    |  ---------
user_id   |  user_id
group_id  |  interest_id

一个用户可以喜欢 0..多个兴趣并属于 0..多个组。

问题：给定一个组 ID，我想获取不属于该组的所有用户的所有兴趣，并且与属于该组的任何人共享至少一个兴趣提供相同的组。

由于上述内容可能令人困惑，这里有一个简单的示例 (SQLFiddle)：

| 1 | 2 | 3 | 4 | 5 | (User IDs)
|-------------------|
| A |   | A |   |   |
| B | B | B |   | B |
|   | C |   |   |   |
|   |   | D | D |   |

在上面的示例中，用户用数字标记，而兴趣用字符标记。

如果我们假设用户 1 和 2 属于组 -1，那么用户 3 和 5 会很有趣：

user_id  interest_id
-------  -----------
      3            A
      3            B
      3            D
      5            B

我已经编写了一个愚蠢且非常低效的查询，可以正确返回上述内容：

SELECT * FROM "interests" WHERE "user_id" IN (
    SELECT "user_id" FROM "interests" WHERE "interest_id" IN (
        SELECT "interest_id" FROM "interests" WHERE "user_id" IN (
            SELECT "user_id" FROM "groups" WHERE "group_id" = -1
        )
    ) AND "user_id" NOT IN (
        SELECT "user_id" FROM "groups" WHERE "group_id" = -1
    )
);

但我所有将其转换为正确连接查询的尝试都表明自己没有结果：查询返回的行数比它应该返回的行多，或者它只需要子查询的 10 倍，例如：

SELECT "iii"."user_id" FROM "interests" AS "iii"
WHERE EXISTS
(
    SELECT "ii"."user_id", "ii"."interest_id" FROM "groups" AS "gg"
    INNER JOIN "interests" AS "ii" ON "gg"."user_id" = "ii"."user_id"
    WHERE EXISTS
    (
        SELECT "i"."interest_id" FROM "groups" AS "g"
        INNER JOIN "interests" AS "i" ON "g"."user_id" = "i"."user_id"
        WHERE "group_id" = -1 AND "i"."interest_id" = "ii"."interest_id"
    ) AND "group_id" != -1 AND "ii"."user_id" = "iii"."user_id"
);

在过去的两个晚上，我一直在努力优化这个查询......

我们将不胜感激任何能让我朝着正确方向前进的帮助或见解。 :)

---

PS：理想情况下，一个返回共同兴趣汇总计数的查询会更好：

user_id  totalInterests  commonInterests
-------  --------------  ---------------
      3               3              1/2 (either is fine, but 2 is better)
      5               1                1

但是，我不确定它与在代码中执行相比会慢多少。

Answer 1

使用以下设置测试表

--drop table Interests  ----------------------------
CREATE TABLE Interests
 (
   InterestId  char(1)  not null
  ,UserId      int      not null
 )

INSERT Interests values
  ('A',1)
 ,('A',3)
 ,('B',1)
 ,('B',2)
 ,('B',3)
 ,('B',5)
 ,('C',2)
 ,('D',3)
 ,('D',4)


--  drop table Groups  ---------------------
CREATE TABLE Groups
 (
   GroupId  int  not null
  ,UserId   int  not null
 )

INSERT Groups values
  (-1, 1)
 ,(-1, 2)


SELECT * from Groups
SELECT * from Groups

以下查询似乎可以满足您的要求：

DECLARE @GroupId int

SET @GroupId = -1

;WITH cteGroupInterests (InterestId)
 as (--  List of the interests referenced by the target group
     select distinct InterestId
      from Groups gr
       inner join Interests nt
        on nt.UserId = gr.UserId
      where gr.GroupId = @GroupId)
--  Aggregate interests for each user
SELECT
   UserId
  ,count(OwnInterstId)      OwnInterests
  ,count(SharedInterestId)  SharedInterests
 from (--  Subquery lists all interests for each user
       select
          nt.UserId
         ,nt.InterestId   OwnInterstId
         ,cte.InterestId  SharedInterestId
        from Interests nt
         left outer join cteGroupInterests cte
          on cte.InterestId = nt.InterestId
        where not exists (--  Correlated subquery: is "this" user in the target group?)
                          select 1
                           from Groups gr
                           where gr.GroupId = @GroupId
                            and gr.UserId = nt.UserId)) xx
 group by UserId
 having count(SharedInterestId) > 0

它似乎有效，但我想做更精细的测试，我不知道它对数百万行的效果如何。重点是：

• cte 创建一个临时表，供后面的查询引用；构建一个实际的临时表可能会提高性能
• 相关的子查询可能很棘手，但索引和not exists 应该会很快完成
• 我很懒，把所有的下划线都省略了，对不起

Answer 2

这有点令人困惑。我认为最好的方法是exists 和not exists：

select i.*
from interest i
where not exists (select 1
                  from groups g
                  where i.user_id = g.user_id and
                        g.group_id = $group_id
                 ) and
      exists (select 1
              from groups g join
                   interest i2
                   on g.user_id = i2.user_id
              where g.user_id <> i.user_user_id and
                    i.interest_id = i2.interest_id
             );

第一个子查询表示用户不在组中。第二个是说兴趣与小组中的某个人共享。