Clustered Index vs Non-Clustered Index in SQL Server

Clustered Index:

• A clustered index determines the physical order of data in a table.
• There can be only one clustered index per table.
• Data rows in a table are sorted and stored in the order of the clustered index key.
• Clustered index is automatically created when the primary key is defined on a table.
• It speeds up data retrieval when the indexed columns are queried.

Non-Clustered Index:

• A non-clustered index does not alter the physical order of the table.
• Multiple non-clustered indexes can be created per table.
• Data rows are stored in a separate structure from the index, pointing back to the clustered index key or row identifier.
• Non-clustered index is recommended for columns that are frequently used in query conditions.
• It incurs additional storage overhead but can improve query performance for specific queries.

Overall, understanding the differences between clustered and non-clustered indexes is crucial for optimizing query performance and data retrieval in SQL Server.