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数据库系统概论2.3 关系的完整性 | Lssyes #21

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Lssyes opened this issue Jun 9, 2021 · 0 comments
Open

数据库系统概论2.3 关系的完整性 | Lssyes #21

Lssyes opened this issue Jun 9, 2021 · 0 comments
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Lssyes commented Jun 9, 2021

https://blog.lssyes.com/2021/03/29/23SQL/

2.3 关系的完整性2.3.1 关系的三类完整性约束 实体完整性和参照完整性： 关系模型必须满足的完整性约束条件，称为关系的两个不变性，应该由关系系统自动支持 用户定义的完整性： 应用领域需要遵循的约束条件，体现了具体领域中的语义约束 2.3.2 实体完整性规则 2.1 实体完整性规则（ Entity Integrity ）若属性 A 是基本关系 R 的主属性，则属性 A ==不能取空值==
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