How can a SQL Query be formulated to include recursive elements?

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In SQL, recursive queries can be formulated using the Common Table Expression (CTE) feature. CTE refers to a temporary result set that can be referenced within an SQL select, update, insert, or delete statement. Here is an example of formulating a recursive SQL query:

1. Create a CTE with an anchor or base case. This defines the starting point of the recursive query.

WITH RECURSIVE cte AS (
  SELECT id, parent_id, name, 0 AS level
  FROM my_table
  WHERE parent_id IS NULL  -- anchor case
)

1. Add a union clause to the CTE, joining the CTE to the original table using a recursive condition. This will append rows to the CTE to build a result set that includes recursive elements.

UNION ALL
SELECT t.id, t.parent_id, t.name, cte.level + 1
FROM my_table t
JOIN cte ON t.parent_id = cte.id

1. Query the CTE to retrieve the final result set.

SELECT id, parent_id, name, level
FROM cte

The final result set will contain all rows from the initial anchor case, joined with all recursive rows that match the join condition. The level column will keep track of how deep each row is in the recursive hierarchy.