Keys
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Keys PowerPoint PPT Presentation


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Keys. Primary Foreign Candidate Surogat Super. Differences. Primary keys: Identifies a single row (unique) Foreign: Identifies a single row in a referenced table. The nature of a key. Surogat : A self invented self genereted key Super

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Keys

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Keys

Keys

Primary

Foreign

Candidate

Surogat

Super


Differences

Differences

Primary keys:

Identifies a single row (unique)

Foreign:

Identifies a single row in a referenced table.


The nature of a key

The nature of a key

  • Surogat:

    A self invented self genereted key

  • Super

    A set of fields that uniquely describe a row

  • Candidate:

    A minimal superkey – it cannot be broken into smaller parts


Wiki s definition

Wiki’s definition

  • In relational database design, a unique key or primary key is a candidate key to uniquely identify each row in a table. A unique key or primary key comprises a single column or set of columns. No two distinct rows in a table can have the same value (or combination of values) in those columns. Depending on its design, a table may have arbitrarily many unique keys but at most one primary key. WRONG!


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