![]() This index also permits fast access to data when the primary key is used in queries. When you specify a primary key constraint for a table, the Database Engine enforces data uniqueness by automatically creating a unique index for the primary key columns. Because primary key constraints guarantee unique data, they are frequently defined on an identity column. This column, or columns, is called the primary key (PK) of the table and enforces the entity integrity of the table. Primary Key ConstraintsĪ table typically has a column or combination of columns that contain values that uniquely identify each row in the table. Primary keys and foreign keys are two types of constraints that can be used to enforce data integrity in SQL Server tables. Applies to: SQL Server 2016 (13.x) and later Azure SQL Database Azure SQL Managed Instance ![]()
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