Oracle – How to Limit Hierarchical Query to Points with Multiple Children

hierarchyoracleoracle-11g-r2

This question is related to my previous question about hierarchical queries.

I have a hierarchical query in Oracle 11gR2 that returns something like this:

- Level 1
  - Level 2
    - Level 3
      - Level 4
        - Level 5
          - Level 6
      - Level 4
        - Level 5
          - Level 6
            - Level 7

I'd like to design a query to return the rows for levels 1-3, on the basis that there are two siblings at level 4. Or, to put it another way, I'd like to return all the rows in the hierarchy, starting from a given point, until I reach a level with more than one sibling. I'd then like to stop there, excluding the level with multiple siblings.

I've tried putting count functions in various places in my query, but I can't work it out. This is what I have so far:

select   *
  from
    (select   level, count (*) over (partition by level) level_count, <columns>
      from <tables>
        start with <predicate>
        connect by prior <child> = <parent>
    )
  where level_count = 1;

This works for the case there the length of each branch is the same, but returns extra rows otherwise. In my example above, I want to return only the rows for levels 1-3 (i.e. 3 rows in total) and exclude level 7 because level 4 has two siblings. I hope that makes sense!

Best Answer

Simplified with window functions:

with hier as
    (select   level as the_level, <columns>
      from <tables>
        start with <predicate>
        connect by prior <child> = <parent>
    ), levels as
    (select hier.*, count(*) over (order by the_level) as count_items
      from hier
    )
  select levels.*
    from levels
    where the_level = count_items ;

Related Solutions

Oracle: How to query a Hierarchical table

FrusteratedWithFormsDesigner has the right direction(+1). Here is what I think you are looking for specifically.

CREATE OR REPLACE VIEW BuildingSubs AS
   SELECT connect_by_root location "Building", location "SubLocation"
   FROM some_table l
   START WITH l.Location IN 
      (
         SELECT location FROM
         (
         SELECT level MyLevel, location FROM some_table 
         START WITH parent IS NULL 
         CONNECT BY PRIOR location=parent
         )
         WHERE MyLevel=3   
      )
   CONNECT BY PRIOR l.location = l.parent;

select * from BuildingSubs; 

Building             SubLocation        
-------------------- --------------------
BLDG-01              BLDG-01              
BLDG-01              Basement             
BLDG-01              Room B-002           
BLDG-01              Floor-01             
BLDG-01              Room 1-001           
BLDG-02              BLDG-02              
BLDG-03              BLDG-03              
Grounds              Grounds

The view accomplishes all three goals. You can query it for a building to find everything it contains and you can query it for a sub-location to find what building it is in.

drop table some_table;
create table some_table (Location Varchar2(20), Parent Varchar2(20));

insert into some_table values ('Org. Name',NULL);
insert into some_table values ('MAINCAMPUS','Org. Name');
insert into some_table values ('BLDG-01','MAINCAMPUS');
insert into some_table values ('BLDG-02','MAINCAMPUS');
insert into some_table values ('BLDG-03','MAINCAMPUS');
insert into some_table values ('Grounds','MAINCAMPUS');
insert into some_table values ('Floor-01','BLDG-01');
insert into some_table values ('Basement','BLDG-01');
insert into some_table values ('Room B-002','Basement');
insert into some_table values ('Room 1-001','Floor-01');

If you don't want to count the building itself as one of the sub-locations you can wrap the existing query in one the eliminates entries in which the building and sublocation are the same.

Reverse connect by prior level value for arbitrarily-deep hierarchy

You can't ever query for ROWNUM = 3; ROWNUM 1 gets filtered out, so the next record is now ROWNUM = 1, and so on.

I suspect being worried about controlling the computational depth is premature optimization. Unless you have millions of options being returned for a single user, pulling the highest level out of the data set - or even pulling the highest level for each dataset should be pretty simple. It's not as if you can't fully explore the hierarchy, so the additional work in the SQL engine of prioritizing/ranking each window of rows is pretty light on top of that.

So using aggregate/window functions seems like a natural choice here.

Your SQLFiddle doesn't return the dataset expected, but I've modified the SQL below to show how you can prioritize them, assuming I understand the requirements you're looking for.

Analytics rock.

select menu_level, menu_name, menu_id
from
(
select menu_level, menu_name, menu_id,
       row_number() over (partition by menu_name order by menu_level desc) as menu_priority
from
(
SELECT
    LEVEL AS menu_level,
    t.name AS menu_name,
    t.id AS menu_id
  FROM
    jhs_menu_items t, (
      SELECT
        jmi.id
      FROM
        jhs_users ju
      JOIN jhs_user_role_grants jurg ON
        ju.id = jurg.usr_id
      LEFT OUTER JOIN user_menu_preferences ump ON
        ju.id = ump.jhs_usr_id
      LEFT OUTER JOIN default_menu_preferences dmp ON
        jurg.rle_id = dmp.jhs_rle_id
      JOIN jhs_menu_items jmi ON
        -- Retrieve the user's preferred menu item, failing to the default
        -- if no preference is set.
        jmi.id = coalesce(
          ump.jhs_menu_items_id,
          dmp.jhs_menu_items_id
        )
      WHERE
        ju.username = 'adminname' 
--      AND ROWNUM = 1
      ORDER BY
        dmp.role_priority_sort
    ) menu_preference

  -- Derive the menu hierarchy starting at the user's preference, going back to 
  -- the root menu item.
  START WITH t.id = menu_preference.id
  CONNECT BY PRIOR t.mim_id = t.id
  )
)
 where menu_priority = 1
 order by menu_name

MENU_LEVEL  MENU_NAME   MENU_ID
        3   MenuTab1    1
        2   MenuTab2    2
        1   MenuTab3    3

Best Answer

Related Solutions

Oracle: How to query a Hierarchical table

Reverse connect by prior level value for arbitrarily-deep hierarchy

Related Question