Preventing infinite loops

Question

Accepted Answer

The standard approach is to carry an array of visited node IDs. In PostgreSQL: anchor starts with ARRAY[id] as visited, recursive member does array_append(visited, e.id) and adds WHERE NOT (e.id = ANY(visited)). This prevents revisiting a node you have already seen. UNION instead of UNION ALL would not help - deduplication removes duplicate output rows but does not stop the recursion from following cycles.