Q25: What is the difference between Clustered and Non-Clustered Indexes?
- Clustered Index: Determines the physical storage order of data rows on disk. Because rows can only be ordered one way, a table can have only one Clustered Index (typically assigned to the Primary Key).
- Non-Clustered Index: A secondary structure stored separately from data rows. It contains indexed column keys and pointers (row IDs or clustered key values) that reference the underlying table rows.
Key Takeaways
- Clustered indexes physically organize table rows on disk; a table can have only one.
- Non-clustered indexes store column keys with pointers back to table data pages.