Primary Key Constraint In SQL Server

The  PRIMARY KEY  constraint in SQL Server ensures that each entry in a table is uniquely recognized.
Primary keys must have UNIQUE values and cannot have NULL values.
In SQL Server, a table can only have one primary key, which can be made up of one or more columns (fields).

What is the primary key in SQL Server?

In SQL Server, a  Primary Key  is a field or column which uniquely identifies each and every record in a table.

    • A primary key column doesn’t allow to insert  null  or duplicate values.
    • A Primary key can consist of up to 16 columns.
    • A table can have only one primary key which can be applied on single or multiple columns.
    • The primary key consist of multiple columns or fields is known as the Composite primary key.
    • A Primary Key constraint can be applied to the columns having any data types.
    • A primary key by default creates a clustered index on the column.

A primary key can be created at the column or table level.

Primary Key Constraint in SQL Server
Primary Key Constraint in SQL Server

Syntax to create a primary key

The following are the syntax to create a primary key in SQL server.

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