Hierarchical Query Child Override - sql

Question

I have a hierarchical company structure where each company has an optional company sector. Child companies inherit their parent's sector if they don't have their own, but the child company sector overrides its parent's if the child one.
I need to produce a sum of the bill amount grouped by sector. Companies with no sector are ignored.
The ParentCompanyID column in the Company table is a foreign key to itself. There can be an unlimited number of parent/child levels.
Company Table
CompanyID ParentCompanyID
1 null
2 1
3 2
4 null
5 4
6 null
7 6
8 7
CompanySector Table
CompanyID Sector
1 Distribution
4 Distribution
5 Manufacturing
8 Manufacturing
Timesheet Table
CompanyID BillAmount
1 100
1 200
2 100
3 50
4 25
5 75
6 75
7 115
8 115
The result I expect to see here is:
Sector BillAmount
Distribution 475
Manufacturing 190
Below is how I am currently doing it. It is extremely inefficient and doesn't work for unlimited number of hierarchical levels.
WITH Company AS
( SELECT 1 CompanyID, NULL ParentCompanyID FROM dual
UNION
SELECT 2, 1 FROM dual
UNION
SELECT 3, 2 FROM dual
UNION
SELECT 4, NULL FROM dual
UNION
SELECT 5, 4 FROM dual
UNION
SELECT 6, NULL FROM dual
UNION
SELECT 7, 6 FROM dual
UNION
SELECT 8, 7 FROM dual
),
CompanySector AS
( SELECT 1 CompanyID, 'Distribution' Sector FROM dual
UNION
SELECT 4 , 'Distribution' FROM dual
UNION
SELECT 5 , 'Manufacturing' FROM dual
UNION
SELECT 8 , 'Manufacturing' FROM dual
),
Timesheets AS
( SELECT 1 CompanyID, 100 BillAmount FROM dual
UNION
SELECT 1 CompanyID, 200 BillAmount FROM dual
UNION
SELECT 2 CompanyID, 100 BillAmount FROM dual
UNION
SELECT 3 CompanyID, 50 BillAmount FROM dual
UNION
SELECT 4 CompanyID, 25 BillAmount FROM dual
UNION
SELECT 5 CompanyID, 75 BillAmount FROM dual
UNION
SELECT 6 CompanyID, 75 BillAmount FROM dual
UNION
SELECT 7 CompanyID, 115 BillAmount FROM dual
UNION
SELECT 8 CompanyID, 115 BillAmount FROM dual
),
--Dummy tables above
--My current way of doing it below
companies AS
(SELECT c.*,
cs.sector
FROM company c
LEFT OUTER JOIN CompanySector cs
ON c.companyID = cs.companyID
),
sectors AS
(SELECT levelOne.companyID,
NVL(levelOne.sector, NVL(levelTwo.sector, NVL(levelThree.sector, NULL))) sector
FROM companies levelOne
LEFT OUTER JOIN companies levelTwo
ON levelOne.parentcompanyid = levelTwo.companyID
LEFT OUTER JOIN companies levelThree
ON levelTwo.parentcompanyid = levelThree.companyID
WHERE NVL(levelOne.sector, NVL(levelTwo.sector, NVL(levelThree.sector, NULL))) IS NOT NULL
)
SELECT s.sector,
SUM(t.billamount)
FROM sectors s
INNER JOIN timesheets t
ON s.companyID = t.companyID
GROUP BY sector;
What is a cleaner and more efficient way of doing this?

Answer 1

I believe this will do it. Using the hierarchical query syntax, populate sector from the parent record where needed.
WITH
base_sectors AS (
SELECT * FROM company LEFT OUTER JOIN companySector USING (companyID)
)
, final_sectors AS (
SELECT companyID, NVL( sector, PRIOR sector ) AS sector
FROM base_sectors
START WITH parentCompanyID IS NULL
CONNECT BY parentCompanyID = PRIOR companyID
)
SELECT s.sector,
SUM(t.billamount)
FROM final_sectors s
INNER JOIN timesheets t
ON s.companyID = t.companyID
GROUP BY sector;