Introduction to Recursive CTE in SQL Server

The Common Table Expressions (CTE) were introduced in SQL Server back in 2005. It is a temporary named result set that can make complex queries simple to write and understand by breaking them into smaller parts. The CTEs can be referenced with INSERT, UPDATE, DELETE, or SELECT statements in SQL. CTE returns a temporary result set that is referenced by another query. As the result set is temporary, it is not stored anywhere in the memory and thus it makes CTE an effective tool that can be used for reference to any other table.

A recursive CTE references itself during the execution. It returns a subset of the result, then it recursively references itself and terminates when it has returned all the results.

Recursive CTEs enable the user to process hierarchical data and allow to join all levels of hierarchy present in the database.

Syntax:

WITH RECURSIVE 
cte_name [(col1, col2, ...)]
AS ( subquery )
Select col1, col2, .. from cte_name;

Explanation of Syntax:

• cte_name: Name given to recursive subquery written in subquery block.

• col1, col2, …colN: The name given to columns generated by subquery.

• Subquery: A MySql query that refer to itself using cte_name as its own name.

CTE which is the abbreviation for Common Table Expression is an SQL Server tool that returns a temporary data set that can be used by another query. In this article, we are going to learn about the Implementation of Recursive CTE in SQL servers. We will understand how recursive common table expressions work step by step and understand their workflow through various examples. Make sure you are familiar with Common table Expressions in SQL before diving into the Recursive CTE’s.