Unclustered Tables

Why You Should Add a Clustered Index to Your SQL Server Tables

In SQL Server, a clustered index is more than just a performance tweak—it’s a fundamental design decision that can significantly impact how your database performs, organizes, and scales. Tables without clustered indexes, often referred to as “heaps,” can lead to inefficiencies and maintenance headaches. In this blog post, we’ll explore why adding a clustered index to a table is a good practice and why heaps can cause problems in SQL Server.

What is a Clustered Index?

A clustered index determines the physical order of data in a table. Unlike a non-clustered index, which is a separate structure pointing to the data, a clustered index is the table itself, with the rows sorted based on the index key. Because of this, a table can have only one clustered index.

When you define a clustered index on a column (or set of columns), SQL Server physically organizes the table’s data in a B-tree structure, where the leaf nodes contain the actual data rows, sorted by the index key.

The Unclustered Tables report shows you tables that do not have a clustered index.