A CTE (Common Table Expression) is used to define a temporary result set which you can use in a SELECT statement. It provides a convenient way to manage complicated queries.
CTE is defined within the statement using the WITH operator. You can define one or more common table expressions like this.
Here is an example of one CTE:
WITH Employee_CTE (EmployeeNumber, Title)
AS
(SELECT NationalIDNumber, JobTitle
FROM HumanResources.Employee)
SELECT EmployeeNumber, Title
FROM Employee_CTE
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