What is the purpose of a clustered index in a database?

The purpose of a clustered index in a database is primarily to sort and store the data rows in the table based on the values of the indexed columns. When a clustered index is created on a table, the database organizes the physical storage of the data according to the order specified by the index. This means that the data itself is stored in sorted order, which can lead to improved performance for both data retrieval operations and range queries, as the database can quickly locate the relevant data in the sorted order.

By sorting the data, the clustered index also allows for efficient retrieval of data, as related rows are stored physically close together on the disk. Hence, while time performance gains can arise indirectly from the sorting capability of a clustered index, the key function lies in organizing the data effectively.

Although clustered indexes can indeed have an impact on performance, their primary role is the physical arrangement of the data in a specific order rather than directly providing speed or reducing storage space. Additionally, the concept of improving overall data security does not accurately relate to the function of a clustered index.