Workflow of Recursive CTE

The workflow of RECURSIVE CTE is majorly consists of these 5 steps:

• Anchor Member Execution: The CTE starts it’s execution with the anchor member which is a non recursive query. It initializes the initial rows of the CTE that serves as the starting point of the recursion.

• Recursive Member Execution(Iterations): The recursive member mainly consists of the SELECT statement that references the CTE itself. Each iteration uses the results that were obtained in the previous iteration or the initial anchor member.This process is repeated until a termination condition is met.

• Termination Condition Check: The termination condition is essential for the termination of the recursive query in the CTE or else our query can get stuck in an infinite loop. This mainly consists of WHERE clause that filters the rows. When the termination condition is met the recursive member halts the execution and returns the result set.

• Union Result Sets: The UNION ALL operator combines the results from the anchor member as well as the results obtained from all of the iterations of the recursive member. At this step the final result set is prepared which will be returned to the user.

• Return Final Result: Finally the result set formed in the previous steps is returned to the user as the output generated by the recursive CTE.

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.