What is a Surrogate Key in SQL?

In database management systems, one of the most critical decisions is choosing the right key to identify and relate data. Surrogate Key is a concept that can help you solve many issues related to data management. It is a unique identifier that has no meaningful attributes and is assigned by the system to ensure data integrity and consistency.

In this article, we will explore everything about Surrogate Key, including its definition, benefits, implementation, and best practices. We’ll also answer some of the most frequently asked questions about this concept.

What is Surrogate Key?

Surrogate Key is an artificial primary key that has no relationship with the actual data it represents. It is a unique identifier that is assigned to each record in a database table to ensure its uniqueness and integrity.

Surrogate Key is also known as a synthetic key, a natural key, or a system-generated key. It is usually created by the system and has no meaningful attributes, such as names, dates, or addresses.

Surrogate Key is used as a primary key to uniquely identify a record in a table. It is independent of any business or application logic and is only used to link records between different tables.

How does Surrogate Key work?

Surrogate Key is generated using a unique sequence generator, a random number generator, or a combination of both. It is usually an integer value, but it can also be a string. The Surrogate Key value is generated automatically by the database management system and is assigned to the record at the time of creation.

The Surrogate Key is stored in a separate column in the database table and is used as the primary key instead of the natural key. The natural key can still be stored in the table for reference purposes, but it is not used as the primary key.

How to Use Surrogate Key?

Using surrogate keys is relatively simple, and involves the following steps-

1. Identify the tables that require surrogate keys.
2. Create a new column for the surrogate keys in each table.
3. Generate a unique value for each record in the table.
4. Use the surrogate keys to link different tables.

Examples of Surrogate Keys

Below are some examples of Surrogate Keys-

1. Auto-Number: This is the most common type of Surrogate Keys used in databases. It is an integer value generated by the database management system and assigned to the record at the time of creation.
2. GUID: GUID (Globally Unique Identifier) is a 128-bit value that provides a unique identifier for each record. It is generated using a combination of timestamps, network addresses, and a random number.
3. UUID: UUID (Universally Unique Identifier) is a 128-bit value that provides a unique identifier for each record. It is generated using a combination of timestamps, network addresses, and a random number.

What are the advantages of a Surrogate Key?

There are several reasons why surrogate keys are used in data management. Some of the key advantages are as follows –

1. Uniqueness: Surrogate keys ensure the uniqueness of each record in the database table, making it easier to manage and update data.
2. Simplified joins: Surrogate keys simplify joins between tables as they provide a unique identifier that can be used to link different tables.
3. Better performance: Surrogate keys can improve performance in large databases as they allow for faster searching and sorting.
4. Confidentiality: Surrogate keys can help to maintain the confidentiality of sensitive data by hiding the natural keys.
5. Data Integrity: Surrogate Keys helps to maintain data integrity by ensuring that each record in a table has a unique identifier.
6. Flexibility: Surrogate Keys provides more flexibility in the database design as it can be changed or updated without affecting other tables or applications.

What are the disadvantages of a Surrogate Key?

Refer to the key disadvantages of Surrogate Key as follows –

1. Overhead: Surrogate Keys adds an overhead to the database, as it requires an additional column to store the Surrogate Keys value.
2. Complexity: Surrogate Keys can make the database more complex, especially when dealing with large tables with multiple relationships.
3. Increased Storage: Surrogate Keys can result in increased storage requirements, as it requires an additional column to store the Surrogate Keys value.

Difference between Surrogate Key and Natural Key

Natural keys are derived from the data itself and are typically used as a primary key in a table. In contrast, surrogate keys are system-generated and are not based on the data in the table. The main difference between natural keys and surrogate keys is that surrogate keys are designed to ensure the uniqueness of each record, while natural keys are based on the data in the table.

Best Practices for Using Surrogate Key

Here are some best practices to follow when using Surrogate Keys-

1. Use an integer data type for the Surrogate Keys column to improve performance and reduce storage space.
2. Don’t use any meaningful attributes for the Surrogate Keys, such as names, dates, or addresses.
3. Use a system-generated sequence or identity column to ensure uniqueness and consistency.
4. Document the Surrogate Keys in the database schema to avoid confusion and mis-interpretation.

How to Create a Surrogate Key in SQL Server

In SQL Server, a surrogate key is a unique identifier assigned to a record in a database table. It’s typically a simple integer value that has no meaning or significance outside of the database. Here’s an example of how you might create a surrogate keys column called “id” in a table called “users” –

Example:

CREATE TABLE users (
  id INT IDENTITY(1,1) PRIMARY KEY,
  username VARCHAR(50) NOT NULL,
  email VARCHAR(100) NOT NULL
);

In this example, the “id” column is declared as an integer and set to “IDENTITY(1,1)”, which means that the database will automatically assign a new, unique value to this column for each new record added to the table, starting at 1 and incrementing by 1 for each new record. The “PRIMARY KEY” constraint is used to specify that the “id” column is the primary key for this table.

Here’s another example that uses a sequence:

Example:

CREATE SEQUENCE orders_seq
START WITH 1
INCREMENT BY 1
NO CACHE;

CREATE TABLE orders (
id INT DEFAULT (NEXT VALUE FOR orders_seq) PRIMARY KEY,
customer_id INT NOT NULL,
order_date DATE NOT NULL
);

In this example, a sequence called “orders_seq” is created to generate unique integer values for the “id” column in the “orders” table. The “START WITH” and “INCREMENT BY” clauses are used to specify the starting value and increment for the sequence, respectively. The “NO CACHE” option is used to ensure that each value generated by the sequence is unique. The “DEFAULT (NEXT VALUE FOR orders_seq)” clause is used to specify that the default value for the “id” column should be the next value in the sequence. The “PRIMARY KEY” constraint is used to specify that the “id” column is the primary key for this table.

We hope this helps! Let me know if you have any more questions.

FAQs

Conclusion

Surrogate Key in SQL is a unique identifier that has no meaningful attributes and is assigned by the system to ensure data integrity and consistency. It is used as a primary key to uniquely identify a record in a table and simplify the join operation between tables. We hope you would have liked this very well.

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