Question

I am trying to query a (large) Oracle 9 table that represents some hierarchical data. The Parent items have their own Id as Parent ID. As an example;

ID    PARENTID               
----- --------  
1     1
2     1
3     2
4     2
5     3
6     6
7     6
8     6
9     4
10    10

I want to have a query that returns each ID, along with the ultimate Parent for that ID, so continuing my example

ID    UlitimateParent
----  ----
1     1
2     1
3     1
4     1
5     1
6     6
7     6
8     6
9     1
10    10

I’ve seen a few examples using Connect By but can’t seem to get this to work. Any ideas ?

Answer 1

In 10g+, you would use the CONNECT_BY_ROOT function:

SQL> with data as (
  2     SELECT 1 id, 1 parent_id FROM DUAL
  3     UNION ALL SELECT 2 , 1  FROM DUAL
  4     UNION ALL SELECT 3 , 2  FROM DUAL
  5     UNION ALL SELECT 4 , 2  FROM DUAL
  6     UNION ALL SELECT 5 , 3  FROM DUAL
  7     UNION ALL SELECT 6 , 6  FROM DUAL
  8     UNION ALL SELECT 7 , 6  FROM DUAL
  9     UNION ALL SELECT 8 , 6  FROM DUAL
 10     UNION ALL SELECT 9 , 4  FROM DUAL
 11     UNION ALL SELECT 10, 10 FROM DUAL
 12  )
 13  SELECT id, connect_by_root(id) ultimate_parent_id
 14    FROM data
 15  START WITH id = parent_id
 16  CONNECT BY parent_id = PRIOR id AND id != PRIOR id  ;

ID  ULTIMATE_PARENT_ID
--- ------------------
  1                  1
  2                  1
  3                  1
  5                  1
  4                  1
  9                  1
  6                  6
  7                  6
  8                  6
 10                 10

In 9i, you could use SYS_CONNECT_BY_PATH (with appropriate substring):

SQL> with data as (
  2     SELECT 1 id, 1 parent_id FROM DUAL
  3     UNION ALL SELECT 2 , 1  FROM DUAL
  4     UNION ALL SELECT 3 , 2  FROM DUAL
  5     UNION ALL SELECT 4 , 2  FROM DUAL
  6     UNION ALL SELECT 5 , 3  FROM DUAL
  7     UNION ALL SELECT 6 , 6  FROM DUAL
  8     UNION ALL SELECT 7 , 6  FROM DUAL
  9     UNION ALL SELECT 8 , 6  FROM DUAL
 10     UNION ALL SELECT 9 , 4  FROM DUAL
 11     UNION ALL SELECT 10, 10 FROM DUAL
 12  )
 13  SELECT id, sys_connect_by_path(id, '->') path
 14    FROM data
 15  START WITH id = parent_id
 16  CONNECT BY parent_id = PRIOR id
 17         AND id != PRIOR id;

        ID PATH
---------- --------------------
         1 ->1
         2 ->1->2
         3 ->1->2->3
         5 ->1->2->3->5
         4 ->1->2->4
         9 ->1->2->4->9
         6 ->6
         7 ->6->7
         8 ->6->8
        10 ->10