Recursive CTE (Common Table Expressions)

Recursive CTEs are a powerful feature in SQL that allow you to build complex hierarchical queries, retrieve data stored in hierarchical structures or even perform graph traversal. In simple terms, a recursive CTE is a CTE that refers to itself in its own definition, creating a loop that iterates through the data until a termination condition is met.

Note that recursive CTEs can be complex, and it's important to ensure a proper termination condition to avoid infinite recursion. Also, be careful with the use of UNION ALL or UNION, as it may impact the results and the performance of your query.