Should You Use Non-Unique Clustered Indexes in Your Database Design?

Considerations for Non-Unique Clustered Indexes in Database Design

In database systems, a clustered index is used to physically order table rows based on the index's key values. While it's generally recommended to make clustered indexes unique, it's not strictly necessary.

Consequences of Non-Unique Clustered Indexes

If a clustered index is not unique, SQL Server resolves duplicates by adding an internally generated "uniqueifier" value. This uniqueifier ensures that each row is assigned a unique identity within the index. However, it introduces additional overhead in calculation and storage.

Impact on Performance

Whether or not this overhead leads to significant performance degradation depends on factors such as:

• Table size
• Insert rate
• Frequency of index usage in queries

Benefits of Unique Clustered Indexes

Making a clustered index unique offers several benefits:

• Eliminates uniqueifiers: Avoiding uniqueifiers reduces index overhead and improves performance.
• Simplifies index maintenance: Unique indexes simplify index operations such as updates and deletes.
• More efficient queries: Queries that utilize unique indexes may benefit from faster execution times.

Recommendation for Non-Unique Clustered Indexes

While non-unique clustered indexes may be used in specific use cases, it's generally advisable to create unique clustered indexes to ensure optimal performance and data integrity. This is particularly important in tables where data changes frequently or where the clustered index is heavily utilized in queries.

The above is the detailed content of Should You Use Non-Unique Clustered Indexes in Your Database Design?. For more information, please follow other related articles on the PHP Chinese website!