What are the differences between a clustered and a non-clustered index in a database?

Differences between a Clustered and a Non-Clustered Index in a Database

When it comes to database indexing, understanding the difference between clustered and non-clustered indexes is crucial for effective database administration. Here are the key differences:

Clustered Index:

• A clustered index determines the physical order of data in a table.
• There can only be one clustered index per table as it directly affects the way data is stored on disk.
• In a clustered index, the leaf nodes of the index contain the actual data pages.
• Due to the physical ordering, retrieving data using a clustered index is generally faster.

Non-Clustered Index:

• A non-clustered index does not affect the physical order of data in a table.
• Multiple non-clustered indexes can be created on a table.
• In a non-clustered index, the leaf nodes of the index contain pointers to the actual data pages.
• Retrieving data using a non-clustered index may require an additional lookup step compared to a clustered index.

Understanding the differences between clustered and non-clustered indexes allows Database Administrators to effectively optimize database performance and query efficiency based on the specific requirements of their applications.