Explain the difference between a clustered index and a non-clustered index in SQL Server.

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Aryan Kumar · Answer

A clustered index is a special type of index in SQL Server that physically orders the data in a table. A non-clustered index is an index that does not physically order the data in a table, but instead stores a pointer to the data in the clustered index.

In SQL Server, each table can have only one clustered index. The clustered index is used to physically order the data in the table, and all queries against the table are executed against the clustered index.

A non-clustered index can be created on any column or set of columns in a table. Non-clustered indexes are used to improve the performance of queries that are frequently executed against a specific column or set of columns.

The main difference between a clustered index and a non-clustered index is that a clustered index physically orders the data in a table, while a non-clustered index does not.

Here is a table that summarizes the differences between clustered indexes and non-clustered indexes:

Feature	Clustered Index	Non-Clustered Index
Number per table	1	Unlimited
Physical order of data	Yes	No
Used for queries	Yes	Yes, for queries on the indexed columns
Storage	Leaf nodes contain the actual data	Leaf nodes contain a pointer to the data in the clustered index

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Explain the difference between a clustered index and a non-clustered index in SQL Server.

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