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What is Surrogate Key in SQL Server?

In SQL Server, a surrogate key is an artificially generated key that is used as a substitute for a natural key (a key based on the attributes of the data itself). It is typically an auto-incremented integer value that has no intrinsic meaning or relation to the data it represents. Surrogate keys are commonly used as primary keys in database tables.

Here are some key points about surrogate keys:

  1. Artificially generated: Surrogate keys are generated by the database system and have no inherent meaning or significance in relation to the data they represent. They are often auto-incremented integers or GUIDs (Globally Unique Identifiers).
  2. Uniqueness: Surrogate keys are designed to be unique within a table, ensuring that no two rows have the same surrogate key value.
  3. Stability: Surrogate keys are typically stable and do not change over time or with updates to the data they represent. This stability helps maintain the integrity of relationships with other tables.
  4. Independence from data attributes: Surrogate keys are independent of the attributes or values of the data. They provide a reliable means of uniquely identifying each row without relying on the actual data values.
  5. Simplified joins and relationships: Surrogate keys simplify the establishment of relationships between tables by providing a consistent and easily joinable identifier.
  6. Performance benefits: Surrogate keys, especially auto-incremented integer keys, can improve performance in certain scenarios, such as indexing and joins, compared to larger or more complex natural keys.

Here's an example of using a surrogate key in SQL Server:


CREATE TABLE Customers (
    CustomerID INT PRIMARY KEY IDENTITY(1,1),
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Email VARCHAR(100)
);

In this example, the "Customers" table has a surrogate key called "CustomerID." It is defined as an auto-incremented primary key using the IDENTITY property. Each new row inserted into the table will automatically be assigned a unique surrogate key value by the database system.

Surrogate keys provide advantages such as simplicity, stability, and improved performance. They allow for consistent and efficient identification of rows, particularly in complex database structures with multiple tables and relationships.

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