What is Primary Key in SQL?

Question

What is Primary Key in SQL?

Answer 1

Primary Key in SQL is a field in the table that helps to identify each row available in the database table in a unique manner. It consists of unique values and it cannot contain null values. Every table can contain only a single primary key that may include one or more fields. If a primary key is a combination of more than a single field then it is a composite key.

Following are some of the features and characteristics of a primary key:

• A table can contain only one primary key
• It consists of at least one column
• It enforces the integrity of the entity in the database table
• None of the columns should contain any null value
• By default, these keys result in unique and clustered indexes

To know more about primary keys, read this comprehensive SQL Tutorial.

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