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School/Development/Foreign Key.md
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# Foreign Key
A Foreign key is a [[Constraint]] that protects links between tables.
A Foreign key is a [[Constraint]] that protects links between tables. Foreign key is a attribute or attributes that link to the [[Primary Key]] of a other entity set (table).
For

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School/Development/Primary Key.md
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# Primary Key
A Primary key is a [[Constraint]] that uniquely identifies [[SQL Database#Entity]] in a entity set (table).
A Primary key is a [[Constraint]] that uniquely identifies [[SQL Database#Entity]] in a entity set (table). Only one pair of values that the primary key forms can exist within a entity set (table).
There can only be ONE primary per table and can consist of multiple attributes (columns).
There als o
A primary key is **not** required, but highly advised. Even if you don't use it its better to include one in your schema.
## Exaple