多对多的关系 [英] many to many relationship

问题描述

如果我有两个表 - table beer 和表分配器，每个都有一个主键和第三具有外键和调用beer_distributor的表。

If I have two tables - table beer and table distributor, each one have a primary key and a third table that have the foreign keys and calls beer_distributor

这个表中的新字段（主键）是否足够？另一种方式是连接，正确吗？要获得例如DUVEL De vroliijke喝酒者？

Is it adequate a new field (primary key) in this table? The other way is with joins, correct? To obtain for example DUVEL De vroliijke drinker?

推荐答案

我将把一个主键放在连接表中 beer_distributor ，而不是两个外键的双主键。 IMO，当维持关系时，它使生活更容易。

I would put a primary key in the join table beer_distributor, not a dual primary key of the two foreign keys. IMO, it makes life easier when maintaining the relationship.

要强调这一点，为啤酒 163 更改分销商 ACOO9 。使用双主键，您必须删除然后重新插入OR或知道两个现有值以更新记录。使用单独的主键，您只需使用此值更新记录。当在这些数据上构建应用程序时很方便。如果这是严格的数据仓库，那么双主键可能从DBA的角度更有意义。

To emphasize this point, consider having to change the distributor ACOO9 for beer 163. With the dual primary key, you'd have to remove then reinsert OR know both existing values to update the record. With a separate primary key, you'd simply update the record using this value. Comes in handy when building applications on top this data. If this is strictly a data warehouse, then a dual primary key might make more sense from the DBA perspective.

UPDATE beer_distributor SET distributor_id = XXXXX WHERE beer_id = 163 AND distributor_id = AC009

对比

UPDATE beer_distributor SET distributor_id = XXXXX WHERE id = 1234

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