What is: The Difference Between a Clustered and a Non-Clustered Index?

A clustered index affects the way the rows of data in a table are stored on disk. When a clustered index is used, rows are stored in sequential order according to the index column value; for this reason, a table can contain only one clustered index, which is usually used on the primary index value.

A non-clustered index does not affect the way data is physically stored; it creates a new object for the index and stores the column(s) designated for indexing with a pointer back to the row containing the indexed values.

You can think of a clustered index as a dictionary in alphabetical order, and a non-clustered index as a book’s index.

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