How to use UNION ALL Operator In SQL
This approach uses the UNION ALL operator to combine the results of the anchor and recursive members within the same CTE. It efficiently traverses the hierarchy.
Example:
WITH RECURSIVE HierarchyCTE AS (
SELECT
ID,
ParentID,
Name,
0 AS Level
FROM
Organization
WHERE
ParentID IS NULL
UNION ALL
SELECT
t.ID,
t.ParentID,
t.Name,
h.Level + 1
FROM
Organization t
JOIN
HierarchyCTE h ON t.ParentID = h.ID
)
SELECT
ID,
ParentID,
Name,
Level
FROM
HierarchyCTE
ORDER BY
Level, ID;
Output:
Recursive Query using UNION ALL Operator
How to Run Hierarchical Queries with PostgreSQL?
In the area of database management, dealing with hierarchical data structures has unique challenges. Whether it’s organizational charts, category hierarchies, or file systems, efficiently querying and traversing hierarchical data is essential for many applications.
PostgreSQL, a powerful relational database management system, offers robust support for handling hierarchical queries through the use of recursive queries and Common Table Expressions (CTEs). In this article, We will learn about