13 lines
584 B
Markdown
13 lines
584 B
Markdown
# Primary Key
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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).
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There can only be ONE primary per table and can consist of multiple attributes (columns).
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A primary key is **not** required, but highly advised. Even if you don't use it its better to include one in your schema.
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## Example
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**Name (PK) - Age - Sex - Length**
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In the table schema above, only one entity where the name is Nick can exist because Name is the primary key.
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