In SQL Server indexing, which index type stores the actual data rows at the leaf (bottom) level and keeps those rows physically ordered the same as the index key?

Introduction / Context:
Choosing between clustered and nonclustered indexes requires knowing where the data lives in the B-tree and how row order is maintained.

Given Data / Assumptions:

• We compare clustered vs nonclustered leaf storage.
• We care about physical order of rows on disk/pages.
• SQL Server implementation is assumed.

Concept / Approach:

In a clustered index, the table data itself is the leaf level of the index, ordered by the clustering key. In a nonclustered index, the leaf contains only keys and locators; data resides elsewhere.

Step-by-Step Solution:

Verification / Alternative check:

Creating a clustered index on a heap converts it into a clustered table; scanning shows order by clustering key.

Why Other Options Are Wrong:

Nonclustered: leaf has pointers, not rows. Primary/Secondary: naming does not define storage semantics.

Common Pitfalls:

Assuming a primary key must be clustered; SQL Server allows a nonclustered primary key.

Final Answer:

Clustered