Understanding Clustered Indexes in SQL

Clustered vs Nonclustered Index

Understanding the difference helps in choosing the right index type for your queries.

• Clustered index stores data rows sorted by the key.
• Nonclustered index stores a separate structure with pointers to data rows.
• Nonclustered indexes can be multiple per table.

How Clustered Indexes Improve Performance

Clustered indexes speed up data retrieval by physically ordering rows, which benefits range queries and sorting operations.

They reduce the need for additional sorting and improve I/O efficiency.

• Faster retrieval for queries using the indexed column.
• Efficient range scans due to ordered data.
• Improved performance for joins on indexed columns.

Creating and Using Clustered Indexes

Most SQL databases create a clustered index automatically on the primary key.

You can create a clustered index explicitly on other columns if needed.

• Syntax example for creating a clustered index:
• Considerations when choosing columns for clustered indexes.