SQL 查找具有公共成员的集合(关系除法) [英] SQL find sets with common members (relational division)

问题描述

我有一组单独的类"和组"，每组都分配了一个或多个标签.我想为每个组找到包含每个组相同(或更多)标签的类的子集.

I have separate sets of "classes" and "groups", each of which has been assigned one or more tags. I would like to find, for each group, the subset of classes that contains the same (or more) tags for each group.

一些示例数据:

declare @Groups table
(
    GroupID int,
    TagID int
)

insert @Groups
values (1,1),(1,2),(1,3),
    (2,1),(2,2),
    (3,1),(3,2),(3,3),(3,4)

declare @Classes table
(
    ClassID int,
    TagID int
)

insert @Classes
values (1,1),(1,2),
    (2,1),(2,2),
    (3,1),(3,2),(3,3)

select * from @Groups
select * from @Classes

和输出:

GroupID TagID
1       1
1       2
1       3
2       1
2       2
3       1
3       2
3       3
3       4

ClassID TagID
1       1
1       2
2       1
2       2
3       1
3       2
3       3

示例结果集如下所示:

declare @Results table
(
    GroupID int,
    ClassID int
)

insert @Results
values (1,3),(2,1),(2,2),(2,3),(3,null)

select * from @Results

结果输出:

GroupID ClassID
1       3
2       1
2       2
2       3
3       NULL

我理解这是一个关系除法类型的问题，涉及have 和count.这些帖子描述了我想要做什么，但我不知道如何将示例应用于上述特定情况:

I understand this is a relational division type problem, involving having and count. These posts describe what I want to do, but I can't figure out how to apply the examples to the particular case above:

• http:///weblogs.sqlteam.com/peterl/archive/2010/07/02/Proper-Relational-Division-With-Sets.aspx
• 仅当所有记录都匹配时才加入 SQL 连接
• 如何构建查询以仅提供与 T-SQL 中 ID 的 CSV 列表中的所有值匹配的行
• SQL:选择包含完全给定成员的集合
• 一个sql查询在定义的集合中查找具有共同标签的用户

推荐答案

我认为这也应该有效

select distinct g.GroupID, c.ClassID
from @Groups g
    left join @Classes c on g.TagID = c.TagID
where not exists (
    select *
    from @Groups g2
    where g2.GroupID = g.GroupID
        and g2.TagID not in (
            select TagID
            from @Classes c2
            where c2.ClassID = c.ClassID
        )
    ) or c.ClassID is null

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