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Using primary keys to improve query performance

A primary key improves performance on the following statement:

SELECT *
FROM Employees
WHERE EmployeeID = 390;

The Plan tab in the Results pane contains the following information:

Employees <Employees>

Whenever the name inside the parentheses on the Plan tab PLAN description is the same as the name of the table, it means that the primary key for the table is used to improve performance.