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Data & Analytics · Intermediate

Clustered Index

An index that determines the physical order in which table rows are stored, so the table itself becomes the index's leaf level.

Definition

Because data can be stored in only one order, a table can have only one clustered index. In SQL Server the primary key creates a clustered index by default. Range queries on the clustered key are efficient. A table without a clustered index is called a heap.

Example

CREATE CLUSTERED INDEX CIX_Sales_Date ON Sales (SaleDate);

Exam tip

One clustered index per table; up to 999 nonclustered indexes in SQL Server.

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