The Relational Model

database
공개

2024년 9월 17일

entity

a formal name for a thing that is being tracked one theme or topic (just single table)

Relation

  • a two-dimensional table that has specific charateristics
  • Cell of the table hold single value
  • All entries in a column are of the same kind
  • No two rows in a table are identical

domain & cartesian product

  • domain: set of possible values for a column
  • cartesian product: set of all possible combinations of rows from two tables

Presenting Relation Structures

RELATION_NAME(PrimaryKey, ForeignKey, ColumnName, …)

key

  • identify a row
  • Unique Key(Primary Key)
  • NonUnique Key(Foreign Key)
  • Composite Key: Primary key가 두개 이상. Surrogate Key로 대체되곤 함.
  • Candidate Key: unique한 columns
  • Surrogate Key: 자동으로 할당되는 일련번호
    IDENTITY (start, increment)

Referential Integrity Constraint

  • 모든 foriegn key는 존재하는 primary key와 매칭되야한다.

Null values

  • required, allow nulls 설정으로 null값을 허용할지 결정
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