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SQL Server FAQ - Difference Between Clustered and Non-Clustered Indexes

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What Is the Difference Between Clustered and Non-Clustered Indexes?

SQL Server 2005 supports two types of indexes: clustered index and non-clustered index. Here are the main differences between them:

• One table can only have only one clustered index.
• One table can only have many non-clustered index.
• A clustered index requires no separate storage than the table storage. It forces the rows to be stored sorted on the index key.
• A non-clustered index requires separate storage than the table storage to store the index information.
• A table with a clustered index is called clustered table. Its rows are stored in a B-Tree structure sorted.
• A table without any clustered indexes is called non-clustered table. Its rows are stored in heap structure unsorted.
• The default index created as part of the primary key column is a clustered index.

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1. What Are Indexes?
2. How To Create an Index on an Existing Table?
3. How To View Existing Indexes on an Given Table using SP_HELP?
4. How To View Existing Indexes on an Given Table using sys.indexes?
5. How To Drop Existing Indexes?
6. Is the PRIMARY KEY Column of a Table an Index?
7. Does the UNIQUE Constraint Create an Index?
8. What Is the Difference Between Clustered and Non-Clustered Indexes?
9. How To Create a Clustered Index?
10. How To Create an Index for Multiple Columns?
11. How To Create a Large Table with Random Data for Index Testing?
12. How To Measure Performance of INSERT Statements?
13. Does Index Slows Down INSERT Statements?
14. Does Index Speed Up SELECT Statements?
15. What Happens If You Add a New Index to Large Table?
16. What Is the Impact on Other User Sessions When Creating Indexes?
17. What Is Index Fragmentation?
18. What Causes Index Fragmentation?
19. How To Defragment Table Indexes?
20. How To Defragment Indexes with ALTER INDEX ... REORGANIZE?
21. How To Rebuild Indexes with ALTER INDEX ... REBUILD?
22. How To Rebuild All Indexes on a Single Table?
23. How To Recreate an Existing Index?