RECURSIVE CTE 

use the recursive CTE to traverse the hierarchical data.

In MySQL, a Recursive Common Table Expression (CTE) is a powerful feature that allows you to create a temporary result set that references itself, enabling it to handle hierarchical data structures like organizational charts or family trees. Recursive CTEs work by running a query multiple times, with each iteration building on the previous result until a specific condition stops the recursion.

Basic Structure of a Recursive CTE

The syntax of a Recursive CTE looks like this:

WITH RECURSIVE cte_name AS (
    
    initial_query  -- anchor member
    
    UNION ALL
    
    recursive_query -- recursive member that references the CTE name
)
SELECT * FROM cte_name;

In this syntax:

• cte_name is the name of the CTE.
• The initial_query is the anchor member, which provides the starting data.
• The recursive_query is the recursive member, which repeatedly works on the result from the previous step (until no new data is found).
• UNION ALL is used to combine the anchor member and the recursive member.

How Recursive CTEs Work

Recursive CTEs consist of two main components:

1. Anchor Member: The starting point that retrieves the initial data.
2. Recursive Member: A query that runs repeatedly, referencing the CTE itself, and continues building the result set.

Execution Process

1. Step 1: The anchor member runs first, creating an initial result set (let's call it R0).
2. Step 2: The recursive member uses the results from R0 to generate the next result set (R1).
3. Step 3: The recursive process continues by using R1 to generate R2, R3, etc.
4. Step 4: This recursion continues until the termination condition is met (i.e., no more data is returned).
5. Step 5: Finally, all the results are combined using the UNION ALL operator.