How does a clustered index differ from a non-clustered index?

A clustered index is crucial in understanding how data is organized within a database table. The uniqueness of a clustered index lies in its ability to dictate the physical order in which data is stored on disk. This means that when a clustered index is created on a table, the data rows themselves are arranged in the order specified by the indexed columns.

This physical arrangement can significantly enhance the performance of queries that retrieve rows based on the clustered index, particularly if those queries involve range searches or ordered results. As a result, the clustered index can lead to improved efficiency for retrieving larger sets of data.

The other options highlight characteristics that do not accurately describe how clustered indexes function. For example, while a clustered index can impact the storage of data, it does not create a separate structure pointing to the data, which is characteristic of non-clustered indexes. It is also important to note that while a database can have only one clustered index, multiple non-clustered indexes can coexist. Additionally, clustered indexes can indeed be created on primary keys, making the last option incorrect.

By understanding the unique role of a clustered index in structuring data storage, you gain insight into how databases optimize data retrieval and management.