Removing duplicate subtrees from CONNECT-BY query in oracle

Question

I have a heirarchical table in the format

CREATE TABLE tree_hierarchy (
  id        NUMBER (20)
 ,parent_id NUMBER (20)
);


INSERT INTO tree_hierarchy (id, parent_id) VALUES (2, 1);
INSERT INTO tree_hierarchy (id, parent_id) VALUES (4, 2);
INSERT INTO tree_hierarchy (id, parent_id) VALUES (9, 4);

When I run the Query:-

SELECT id,parent_id,
  CONNECT_BY_ISLEAF leaf,
  LEVEL,
  SYS_CONNECT_BY_PATH(id, '/') Path,
  SYS_CONNECT_BY_PATH(parent_id, '/') Parent_Path
FROM tree_hierarchy
WHERE CONNECT_BY_ISLEAF<>0
  CONNECT BY PRIOR id = PARENT_id
ORDER SIBLINGS BY ID;

Result I am Getting is like this:-

"ID"    "PARENT_ID" "LEAF"  "LEVEL" "PATH"  "PARENT_PATH"

9            4         1       3    "/2/4/9"  "/1/2/4"

9            4         1       2     "/4/9"     "/2/4"

9            4         1       1      "/9"      "/4"

But I need an Oracle Sql Query That gets me only this

"ID"    "PARENT_ID" "LEAF"  "LEVEL" "PATH"  "PARENT_PATH"

9            4         1       3    "/2/4/9"  "/1/2/4"

This is a simpler example I have more that 1000 records in such fashion.When I run the above query,It is generating many duplicates.Can any one give me a generic query that will give complete path from leaf to root with out duplicates.Thanks for the help in advance

Answer 1

The root node in finite hierarchy must be always known. According to the definition: http://en.wikipedia.org/wiki/Tree_structure the root node is a node that has no parents. To check if a given node is a root node, take "parent_id" and check in the table if exists a record with this id. The query might look like this:

SELECT id,parent_id,
  CONNECT_BY_ISLEAF leaf,
  LEVEL,
  SYS_CONNECT_BY_PATH(id, '/') Path,
  SYS_CONNECT_BY_PATH(parent_id, '/') Parent_Path
FROM tree_hierarchy th
WHERE CONNECT_BY_ISLEAF<>0
  CONNECT BY PRIOR id = PARENT_id
START WITH not exists (
      select 1 from tree_hierarchy th1 
      where th1.id = th.parent_id
  )
ORDER SIBLINGS BY ID;