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School/Development/Foreign Key.md
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# Foreign Key # 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 # 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 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. 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