Question

The question is pretty trivial I guess. But nevertheless, E.g., I have Entities: user (id, name), group (id, name), user_group (user_id, group_id) and gallery (id, name, owner_id). Owner of the gallery could be user OR group.

如何在关系数据库中找到最佳解决办法?

感谢!

PS 任何人都知道如何优化使用 al和chem。它如何看待?

我想到的是所有权人(id,user_id, group_id),但我对如何显示关系方面的“OR”关系没有任何想法。

Answer 1

The simplest solution would be a relation Owner(id, user_id, group_id) where either user_id or group_id can be set -- guard that with an appropriate constraint.

缩略语

A group could have not only users but other groups (recursion and/or infinit cylces ahead).
If User and Group are used in some more places more adaptions might be necessary.
Data consistence cannot be enforced by the database any more.

Answer 2

Combine Owner and group into one table. 所有人和群体只能因本表的属性而有所不同,或者在结合本新表格(“成员”)时有/没有行踪。

Answer 3

用户与群体之间不存在技术差异(只有概念一)。

将这两条列入同一表格(user),并在第二个领域标明一个浏览类型(组群或用户)。

使用应用逻辑,确保只有group的“有子女”才能列入user_group表。

Answer 4

引进一个新实体,使其成为小组的所有人。然后,将电离层和组群的类别(即“继承”的类别)放出。

Your ER model would look like this (only PK fields shown):

enter image description here

从理论上讲,在物理数据库中采用一种类别有三种主要方法。所有这一切都有利弊,但就你的模式而言,solution 1可能是最适当的:

Use separate tables for OWNER, USER and GROUP and connect them via FOREIGN KEYs.
- In this scenario, you may or may not use the discriminator (i.e. type identifier) in OWNER.
Put USER and GROUP in the separate tables, with OWNER s fields present in both.
Put OWNER, USER and GROUP in the same table.

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