Surrogate Key in DBMS
A Surrogate Key in a Database Management System (DBMS) is a unique identifier for a record that has no real-world meaning. It is typically an artificially created key used to uniquely identify rows in a table. Surrogate keys are usually simple, such as an automatically generated number, and are not derived from any actual data in the table.
Important: In many cases, the terms Surrogate Key and Artificial Key are used interchangeably because both are system-generated, unique, and have no real-world meaning. However, Surrogate Key is a more specific term often used in complex data models and data warehousing, while Artificial Key is a broader term that simply refers to any key created by the system to identify records.
Why Use a Surrogate Key?
Surrogate keys are used to avoid complications when natural keys (keys based on real-world data) are too complex, changeable, or have null values. Surrogate keys provide a simple, stable, and non-changing way to uniquely identify records.
Example of a Surrogate Key
Consider a Customer table:
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Columns: CustomerID, FirstName, LastName, Email
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CustomerID could be a Surrogate Key: It’s an automatically generated number, like 1, 2, 3, and so on. This key doesn’t have any real-world meaning but serves as a unique identifier for each customer.
If you used Email as the primary key, it could change, or two customers might share the same email, which is problematic. By using CustomerID as a surrogate key, you avoid these issues.
Characteristics of a Surrogate Key
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Artificial: It has no real-world meaning and is usually automatically generated.
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Unique: Each record has a unique surrogate key value.
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Non-changeable: Once assigned, it doesn’t change, unlike natural keys that can change over time.
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Simpler than natural keys: Surrogate keys are often simpler and easier to use in relationships than complex natural keys.
When to Use a Surrogate Key?
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When natural keys are too complex or have changing values.
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When NULL values are present in the natural key column, but you still need a unique identifier.
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When you want to simplify your database design and avoid the complexities of using data-driven keys.
Advantages of Surrogate Keys
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Simplified Relationships: Surrogate keys make it easier to set up relationships between tables.
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Consistency: They provide a stable identifier that doesn’t change, unlike real-world data.
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Better Performance: Surrogate keys are usually smaller (often integers), which can improve query performance.
Disadvantages of Surrogate Keys
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Lack of Meaning: Since they don’t reflect real-world data, surrogate keys might not be useful for interpreting the data.
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Additional Complexity: While they simplify the structure, surrogate keys add an extra layer of abstraction.
Conclusion
A Surrogate Key in DBMS is a useful tool for ensuring that every record has a unique, stable identifier without relying on real-world data. They help simplify database design and make it easier to manage relationships between tables, particularly when natural keys are complicated or unreliable.