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Learn Computer Science
Developing a more interesting World
"Computer science is no more about computers than astronomy is about telescopes."
Edsger Dijkstra
Free beginner - intermediate level computer science tutorials
Keys
There are 4 types of keys we will learn here:
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Primary Key
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Foreign Key
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Candidate Key
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Super Key
Primary Key
A Primary Key :
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uniquely defines each row's characteristics.
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can not be duplicated by other rows.
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is not allowed NULL values.
Super Key
Foreign Key
A Foreign Key:
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is an "ambassador" for another table's Primary Key.
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is intended to match another table's Primary Key.
Candidate Key
A Candidate Key is a column or set of columns that uniquely identify any row without any data.
A Super Key is a combination of attributes that determines ALL the other attributes in the table i.e. determines a whole row.
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