What is the difference between a clustered and a non-clustered index in SQL Server?

Clustered vs. Non-Clustered Index in SQL Server

In SQL Server, a clustered index determines the physical order of the data in a table. It affects the way records are stored on disk, as the data is physically arranged according to the order of the clustered index key. Each table can have only one clustered index, and it is recommended for tables that are frequently accessed using range queries or when the data is commonly retrieved in a specific order.

On the other hand, a non-clustered index does not affect the physical order of the data in the table. Instead, it stores the index key values along with pointers to the corresponding data rows. This allows for faster retrieval of data based on the indexed columns. A table can have multiple non-clustered indexes, making them suitable for columns that are frequently used in search queries but not for sorting or ordering data.

In summary, the key differences between a clustered and a non-clustered index in SQL Server are:

• Clustered index determines the physical order of data, while a non-clustered index does not.
• Each table can have only one clustered index, but multiple non-clustered indexes.
• Clustered indexes are recommended for range queries and specific order retrieval, while non-clustered indexes are suitable for search queries.

Understanding the differences between clustered and non-clustered indexes can help optimize the performance of database queries and improve the overall efficiency of data retrieval in SQL Server.