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What is a Primary Key?

The PRIMARY KEY constraint uniquely identifies each record in a database table.

Primary keys must contain unique values.

A primary key column cannot contain NULL values.

Each table should have a primary key, and each table can have only ONE primary key.

The primary key is defined by using the PRIMARY KEY constraint when either creating a table or altering a table.

*Example of primary key :- customer No

what is its purpose and why do you use it?

In relational database design, a unique key or primary key is a candidate key to uniquely identify each row in a table.

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