我应该使用多个到许多“链接”中的索引列。表？ [英] Should I use an index column in a many to many "link" table?

问题描述

我有两个表，产品和类别有多对多的关系，所以我添加将包含 category_id 和 product_id 的 products_categories / p>

我应该添加另一个（自动递增）索引列还是使用两个现有索引列作为主键？

$ p
$ b

• 你看到的数据更多的是一组对象关系数据库只是
  a存储介质）或者通过关系代数原生表示和分析的事实集合。




• 一些ORM /框架/工具没有对多列主键的良好支持。
  如果你碰巧使用其中的一个，你将需要额外的id列。




• 如果它只是一个多对多关系没有额外的数据相关联，
  最好避免额外的id列，并将两列作为主键。




• 对这个关联的附加信息，那么它将变成
  ，然后两个实体的多对多关系。
  所以它成为它自己的实体，如果它有自己的id
  独立于它连接的实体会更方便。

I have two tables, products and categories which have a many to many relationship, so I'm adding a products_categories table which will contain category_id and product_id.

Should I add another (auto-incrementing) index column or use the two existing ones as primary key?

解决方案

That depends.

• Are you seeing your data more as set of objects (and relational database is just a storage medium) or as set of facts represented and analyzed natively by relational algebra.

• Some ORMs/Frameworks/Tools don't have good support for multicolumn primary keys. If you happen to use one of them, you'll need additional id column.

• If it's just a many-to-many relationship with no additional data associated with it, it's better to avoid additional id column and have both columns as primary key.

• If you want to add some additional information to this association, then it'll become something more then many-to-many relationship of two entities. So it becomes entity in it's own and it'd be more convenient if it had it's own id independent to entities it connects.

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