Oracle analytic function - using FIRST_VALUE to remove unwanted rows

Question

I believe the Oracle function FIRST_VALUE is what I need to be using based on these two questions: SQL - How to select a row having a column with max value
Oracle: Taking the record with the max date

I have 3 tables that represent people associated with organizations. Each organization may have a parent org, where ORG.PARENT is a foreign key to ORG.ID (so the table refers to itself). A person may be associated with more than one group.

PERSON

ID    NAME
----------
1     Bob

ORG

ID    NAME        PARENT
------------------------
1     A           (null)
2     A-1              1
3     A-2              1
4     A-3              1
5     A-1-a            2
6     A-1-b            2
7     A-2-a            3
8     A-2-b            3

PERSON_TO_ORG

PERSON_ID  ORG_ID
-----------------
    1        1
    1        3

I want to list the groups a person is associated with so I used this query:

SELECT NAME, ID, sys_connect_by_path(NAME, '/') AS path
FROM org
START WITH ID IN
(SELECT org_id FROM person_to_org WHERE person_id=1)
connect by prior org.ID = org.parent;

...which gives me:

NAME    ID    PATH
------------------
A-2     3     /A-2
A-2-a   8     /A-2/A-2-a
A-2-b   9     /A-2/A-2-b
A       1     /A
A-1     2     /A/A-1
A-1-a   5     /A/A-1/A-1-a
A-1-b   6     /A/A-1/A-1-b
A-2     3     /A/A-2
A-2-a   8     /A/A-2/A-2-a
A-2-b   9     /A/A-2/A-2-b
A-3     4     /A/A-3

Notice how A-2 appears twice, as it should. I don't want a group to appear twice, however. I want a group to only appear at its lowest level in the tree, i.e. at its highest level value. Here is how I've tried using FIRST_VALUE with no luck - I still get A-2 (and others) appearing twice:

SELECT id, name, path, first_value(lev) OVER
(
PARTITION BY ID,NAME, path ORDER BY lev DESC
) AS max_lev FROM
(SELECT NAME, ID, sys_connect_by_path(NAME, '/') AS path, LEVEL as lev
FROM org START WITH ID IN
(SELECT org_id FROM person_to_org WHERE person_id=1)
connect by prior org.ID = org.parent);

This seems similar to the FIRST_VALUE example in Pro Oracle SQL but I can't seem to make it work no matter how I tweak the parameters.

How can I return only the rows where a given group has its highest level value (i.e. farthest down in the tree)?

Answer 1

As also said in one of the threads you refer to, analytics are not the most efficient way to go here: you need to aggregate to filter out the duplicates.

SQL> SELECT id
  2       , max(name) keep (dense_rank last order by lev) name
  3       , max(path) keep (dense_rank last order by lev) path
  4    FROM ( SELECT NAME
  5                , ID
  6                , sys_connect_by_path(NAME, '/') AS path
  7                , LEVEL as lev
  8             FROM org
  9            START WITH ID IN (SELECT org_id FROM person_to_org WHERE person_id=1)
 10          connect by prior org.ID = org.parent
 11         )
 12   group by id
 13  /

        ID NAME  PATH
---------- ----- --------------------
         1 A     /A
         2 A-1   /A/A-1
         3 A-2   /A/A-2
         4 A-3   /A/A-3
         5 A-1-a /A/A-1/A-1-a
         6 A-1-b /A/A-1/A-1-b
         7 A-2-a /A/A-2/A-2-a
         8 A-2-b /A/A-2/A-2-b

8 rows selected.

Regards,
Rob.

PS: Here is some more information about the LAST aggregate function: http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions071.htm#sthref1495

Answer 2

You should partition only OVER (PARTITION BY ID,NAME ORDER BY lev DESC) not ID,NAME, path

Edit: And probably you want first_value(path), not first_value(lev)

Answer 3

What about this (untested)

SELECT 
    SELECT id, 
           name, 
           path
FROM (            
    SELECT id, 
           name, 
           path, 
           row_number() over (partition by id,name order by lev desc) as rn
    FROM (
       SELECT NAME, 
              ID, 
              sys_connect_by_path(NAME, '/') AS path, 
              LEVEL as lev
       FROM org 
       START WITH ID IN (SELECT org_id FROM person_to_org WHERE person_id=1)
       connect by prior org.ID = org.parent
    )
) 
where rn = 1