How to find the id of the node given the path using connect by?

Question

I have a table like this:
CREATE TABLE tab1 (Id INTEGER, Name VARCHAR2(100), ParentId INTEGER)
Let's say I have the following rows:
Id name ParentId
1 X NULL
2 Y 1
3 Z 2
4 A 3
Now, given the path /X/Y/Z/A, I need to return 4
Is it possible to achieve this using CONNECT BY?
If it helps, I have over simplified the scenario - that a node has only one child. In reality, a node can have many children.
Thanks.

Answer 1

Hi,
user2888313 wrote:
Thanks for the suggestions - will follow from now on. Here's one way to post the sample data, given the CREATE TABLE statement you posted earlier:
-- Basic data:
INSERT INTO tab1 (id, name, parentid) VALUES (1,  'X', NULL);
INSERT INTO tab1 (id, name, parentid) VALUES (2,  'Y', 1);
INSERT INTO tab1 (id, name, parentid) VALUES (3,  'Z', 2);
INSERT INTO tab1 (id, name, parentid) VALUES (4,  'A', 3);
-- To test branching (i.e., multiple children for the same parent):
INSERT INTO tab1 (id, name, parentid) VALUES (11, 'P', 1);
INSERT INTO tab1 (id, name, parentid) VALUES (12, 'Q', 1);
INSERT INTO tab1 (id, name, parentid) VALUES (13, 'R', 12);Alternatively, you could post a WITH clause, as someone did above.
I am not clear how to use the LEVEL pseudo column. Should I just start from the root, find all paths up to the level I am looking for? Could you please give me the syntax? Sorry, I'm still not clear what you want, or why you want it.
Do you want 4 because 'A' is the 4th generation in this family tree (that is, because 'A' has 3 ancestors), or do you want 4 because id=4 is on the same row as name='A'? In the former case, use LEVEL; in the latter, use the id column.
This query shows both:
SELECT  SYS_CONNECT_BY_PATH (name, '/')          AS name_path
,     LEVEL                                AS lvl
,     id
FROM     tab1
START WITH     parentid     IS NULL
CONNECT BY     parentid     = PRIOR id
;Output from the expanded sample data:
NAME_PATH                   LVL         ID
/X                            1          1
/X/Y                          2          2
/X/Y/Z                        3          3
/X/Y/Z/A                      4          4
/X/P                          2         11
/X/Q                          2         12
/X/Q/R                        3         13