oracle hierarchy that gets wrong reference parent - sql

Question

I have the below data example for some items, those items have reference and reference parents. My issue is some references have wrong parents,which lead to infinite loop
let me explain, item with reference K001 doesn't have reference because it is the main product, reference k002 its parent is k001. k003 its parents is k001, data here is correct, because k001 is the parent with reference First.
For type B data is incorrect, m992 its parent is m993, however reference m993 its parent is m992, this is incorrect, the reference should point to a reference_parent First so to fix this the reference_parent for reference m992 should be m991 not m993.
For type C data also is incorrect, reference K883 has wrong reference_Parent because it hask886.
Because when I go to reference K886 I check its reference parent which is k885 then i check k885 reference parent which is k884 , then i check reference parent for k884 which is k883, then when I check k883 reference parent it gives me k886, here its wrong and I go an infinite loop, because k886 reference parent is kk85. To correct the reference parent of item k883 should be k882
Type Reference Reference_Parent
A K001 First
A K002 K001
A K003 K001
B M991 First
B M992 M993 --wrong parent data
B M993 M992
C K881 First
C K882 K881
C K883 K886 --wrong parent data
C K884 K883
C K885 K884
C K886 K885
A L001 First
A L002 L001
A L003 L002
A L004 L002
A L005 L002
A L006 L004
I tried with below query but its not giving me my required result and I am not expert with heirachy queries
SELECT reference,reference_parent,LEVEL ,SYS_CONNECT_BY_PATH(reference, '/') "Path"
FROM ITEMS
WHERE TYPE='B'
START WITH reference_parent = 'First'
CONNECT BY nocycle PRIOR reference_parent = 'First'
My required result is to give me
B M992 M993 --wrong parent data
C K883 K886 --wrong parent data

Answer 1

Oracle Setup:
CREATE TABLE ITEMS ( Type, Reference, Reference_Parent ) AS
SELECT 'A', 'K001', 'First' FROM DUAL UNION ALL
SELECT 'A', 'K002', 'K001' FROM DUAL UNION ALL
SELECT 'A', 'K003', 'K001' FROM DUAL UNION ALL
SELECT 'B', 'M991', 'First' FROM DUAL UNION ALL
SELECT 'B', 'M992', 'M993' FROM DUAL UNION ALL --wrong parent data
SELECT 'B', 'M993', 'M992' FROM DUAL UNION ALL
SELECT 'C', 'K881', 'First' FROM DUAL UNION ALL
SELECT 'C', 'K882', 'K881' FROM DUAL UNION ALL
SELECT 'C', 'K883', 'K886' FROM DUAL UNION ALL --wrong parent data
SELECT 'C', 'K884', 'K883' FROM DUAL UNION ALL
SELECT 'C', 'K885', 'K884' FROM DUAL UNION ALL
SELECT 'C', 'K886', 'K885' FROM DUAL UNION ALL
SELECT 'A', 'L001', 'First' FROM DUAL UNION ALL
SELECT 'A', 'L002', 'L001' FROM DUAL UNION ALL
SELECT 'A', 'L003', 'L002' FROM DUAL UNION ALL
SELECT 'A', 'L004', 'L002' FROM DUAL UNION ALL
SELECT 'A', 'L005', 'L002' FROM DUAL UNION ALL
SELECT 'A', 'L006', 'L004' FROM DUAL;
Query:
SELECT DISTINCT
MIN( CONNECT_BY_ROOT( Reference_Parent ) )
KEEP ( DENSE_RANK FIRST ORDER BY CONNECT_BY_ROOT( Reference ) )
AS reference_parent,
MIN( CONNECT_BY_ROOT( Reference ) )
AS reference
FROM ITEMS
START WITH Reference NOT IN (
SELECT reference
FROM ITEMS
START WITH Reference_Parent = 'First'
CONNECT BY PRIOR Reference = Reference_Parent
)
CONNECT BY NOCYCLE PRIOR Reference = Reference_Parent
GROUP BY Reference
Output:
REFERENCE_PARENT | REFERENCE
:--------------- | :--------
K886 | K883
M993 | M992
db<>fiddle here
Explanation:
You can find all the rows in the hierarchy starting with 'First' using the query:
SELECT reference
FROM ITEMS
START WITH Reference_Parent = 'First'
CONNECT BY PRIOR Reference = Reference_Parent
Your rows will be disconnected from these so you want a hierarchical query like:
SELECT *
FROM ITEMS
START WITH Reference NOT IN (
SELECT reference
FROM ITEMS
START WITH Reference_Parent = 'First'
CONNECT BY PRIOR Reference = Reference_Parent
)
CONNECT BY NOCYCLE PRIOR Reference = Reference_Parent
This just gives you the disconnected components and will generate lots of duplicate rows as it will start the hierarchy at every point in the cycle so some additional work is required to find the lowest Reference in the cycle (which appears to be where you are saying the wrong parents have occurred). This can be found by getting the MINimum values for CONNECT_BY_ROOT( Reference ) for each Reference; which gives you the query above.
Query 2:
You could also just look for cycles without eliminating the rows connected to 'First':
SELECT DISTINCT
MIN( Type ) KEEP ( DENSE_RANK FIRST ORDER BY Reference )
AS Type,
MIN( Reference ) AS Reference,
MIN( Reference_Parent ) KEEP ( DENSE_RANK FIRST ORDER BY Reference )
AS Reference_Parent
FROM (
SELECT Type,
Reference,
Reference_parent,
CONNECT_BY_ROOT( Reference_Parent ) AS root_reference_parent,
CONNECT_BY_ROOT( Reference ) AS root_reference,
CONNECT_BY_ISCYCLE AS isCycle
FROM ITEMS
CONNECT BY NOCYCLE PRIOR Reference = Reference_Parent
)
GROUP BY
root_Reference,
root_Reference_Parent
HAVING MAX( isCycle ) = 1
db<>fiddle here