SQL

Traverse Hierarchical Data with Recursive CTE

Query tree-like or hierarchical data structures (e.g., categories, comments, organizational charts) using a Common Table Expression (CTE) to traverse parent-child relationships.

WITH RECURSIVE CategoryPath AS (
  SELECT id, name, parent_id, CAST(name AS VARCHAR(255)) AS path
  FROM categories
  WHERE parent_id IS NULL
  UNION ALL
  SELECT c.id, c.name, c.parent_id, CAST(cp.path || ' -> ' || c.name AS VARCHAR(255))
  FROM categories c
  JOIN CategoryPath cp ON c.parent_id = cp.id
)
SELECT id, name, parent_id, path FROM CategoryPath ORDER BY path;

How it works: This snippet uses a `WITH RECURSIVE` Common Table Expression (CTE) to traverse hierarchical data, such as a category tree. The 'anchor member' selects the root categories (those without a parent). The 'recursive member' then repeatedly joins back to the CTE to find children of the previously found categories, building a full path for each category. This is powerful for displaying nested data structures in web applications.

Traverse Hierarchical Data with Recursive CTE

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