Explanation of Find Tables Without Clustered Index in SQL Server

A clustered index defines the physical order of data in a table. It is important for performance, especially when working with large datasets. Tables without a clustered index are called heaps, and they can lead to poor performance in queries and maintenance operations like updates or deletes.

You can use a script to find all user tables in your database that do not have a clustered index.

Example Script:

1. SELECT   
2.     s.name AS SchemaName,  
3.     t.name AS TableName  
4. FROM   
5.     sys.tables t  
6. JOIN   
7.     sys.schemas s ON t.schema_id = s.schema_id  
8. WHERE   
9.     NOT EXISTS (  
10.         SELECT 1   
11.         FROM sys.indexes i   
12.         WHERE i.object_id = t.object_id   
13.         AND i.type = 1 -- Clustered Index  
14.     )  
15. ORDER BY   
16.     s.name, t.name;  

Conclusion:

This script helps identify heap tables (tables without a clustered index) in your SQL Server database. Adding a proper clustered index to these tables can improve query performance, data integrity, and maintenance efficiency. Regularly reviewing heap tables is a good practice in database optimization.