Can you explain the differences between a clustered and non-clustered index in a database and when would you choose to use each one?

Clustered vs Non-Clustered Index in a Database

A clustered index sorts and stores the data rows in the table based on the key values, and there can be only one clustered index per table. This means that the physical order of the rows in the table matches the order of the key values in the index. On the other hand, a non-clustered index does not alter the order of the rows in the table and instead creates a separate structure to store the indexed columns along with a pointer to the actual row.

When to use a clustered index:

• Use a clustered index when you frequently search for ranges of data or need to sort the data based on a specific column.
• Clustered indexes are beneficial for read-heavy operations as they can improve the performance of queries that involve sorting and range queries.
• Clustered indexes are ideal for columns with unique or non-null values as they enforce data integrity through their uniqueness.

When to use a non-clustered index:

• Use a non-clustered index when you need to improve query performance for columns that are frequently searched but do not require sorting or unique constraints.
• Non-clustered indexes are suitable for columns with low selectivity and where data modifications are infrequent.
• Non-clustered indexes can help optimize queries that involve joins, filtering, or searching in a specific column.

It is essential to consider the specific requirements of your database and query patterns when choosing between a clustered and non-clustered index to ensure optimal performance and data accessibility.