alternate key

最新推荐文章于 2025-06-02 09:07:22 发布

amber112

最新推荐文章于 2025-06-02 09:07:22 发布

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分类专栏： oracle 文章标签： attributes database table

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本文介绍了在关系数据库中候选键的概念及其与主键的关系。通过具体例子说明了如何区分候选键与被选作主键的候选键，即替代键。

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alternate key 候选键、替代键

In the context of relational databases, an alternate key (or secondary key) is any candidate key which is not selected to be the primary key (PK).

For example, a relational database with a table "employee" could have attributes like "employee_id", "national_insurance_number", and so on. In this case, both "employee_id" and "national_insurance_number" serve as unique identifiers for a given employee, and could thus arguably be used for a primary key. Hence, both of them are called "candidate keys". If, for example, "national_insurance_number" was chosen as the primary key, "employee_id" would become the alternate key.