Relational Model

基本结构

• 一张表对应一个关系 (relation)，行对应元组 (tuple)，列对应属性 (attribute)
• 码 key
  • Let $K\subseteq R$
  • $K$ is a superkey of $R$ is values for $K$ are sufficient to identify a unique tuple of each possible relation
  • $K$ is a condidate key is $K$ is minial superkey
  • $K$ is a primary key, if K is a candidate key and is defined by user explicitly
  • Foreign key Assume there exists relations $r$ and $s$: $r(A,B,C)$, $s(B,D)$, we can say that attribute $B$ in relation $r$ is foreign key referencing $s$, and $r$ is a referencing relation, and $s$ is a referenced relation.

关系代数

关系代数是 Relational Model 的数学基础，详见 Relational algebra

SQL

SQL：结构化查询语言，分为 DDL,DML,DCL 几种类型，详见 SQL