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Stairway to Advanced T-SQL Level 3: Understanding Common Table Expressions (CTEs)

2015/03/18

(http://www.sqlservercentral.com/articles/Stairway+Series/122606/)

The Series

This article is part of the Stairway Series: Stairway to Advanced T-SQL

This stairway will contain a series of articles that will expand on the T-SQL foundation that you learned in the prior two T-SQL stairways, Stairway to T-SQL DML and T-SQL Beyond the Basics. This stairway should help readers prepare for passing the Microsoft Certification exam 70-461: Querying Microsoft SQL Server 2012.

With the rollout of SQL Server 2005, Microsoft introduced a new query construct called a common table expression (CTE). A CTE is a temporary result set defined by a simple query, and is used within the execution scope of a single INSERT, UPDATE, DELETE, or SELECT statement. In this article I be exploring how to define and use CTE's.

Defining and Using CTE's

With the introduction of CTE's by Microsoft you now have a different way to build and document complex pieces of TSQL code. By using a CTE you can write and name a TSQL SELECT statement and then reference the named statement later on much like you would reference a table or a view.

Below is the syntax for defining a CTE:

WITH <expression_name> (Column1, Column2, …) AS (CTE Definition)

Where: