A clustered index is used to define the order or to sort the table or arrange the data by alphabetical order just like a dictionary. A non-clustered index collects the data at one place and records at another place. It is faster than a non-clustered index. It is slower than the clustered index.

In brief, the main differences between a cluster and non-cluster index are:

Clustered Index:

• Determines the physical order of data in a table.
• Each table can have only one clustered index.
• Data is physically reorganized to match the order of the clustered index.
• Useful for frequent retrieval of data in a specific order.
• Updating or inserting data can be more resource-intensive.

Non-Clustered Index:

• Does not affect the physical order of data in a table.
• Multiple non-clustered indexes can be created on a single table.
• Provides a separate structure to efficiently access data.
• Useful for optimizing specific queries by providing quick data access.
• Updating or inserting data is generally less resource-intensive.

The choice between them depends on the specific requirements of data retrieval and the balance between query performance and data modification operations.