Can Hierarchical queries be used in a condition? - sql

Question

I am going to build a Hierarchial Tree in Oracle Forms using the Hiearchical queries. As far as I know, the HQ works only for single table, can they be used in a condition where we have Master Details scenario.
Or can it be based on a view?
For example; I want to display an hierarchical with 3 of options from various tables. For example a Customer Order can have have various Items. First List of All CO, on clicking a specific CO, All the Items therein, An Item may have Sub Parts, and so on. Spanning multiple connected tables

Answer 1

If you have the test data:
CREATE TABLE customer_orders ( id, name ) AS
SELECT 1, 'Cust. Ord. XYZ' FrOM DUAL UNION ALL
SELECT 2, 'Cust. Ord. ABC' FrOM DUAL UNION ALL
SELECT 3, 'Cust. Ord. MNO' FrOM DUAL;
CREATE TABLE customer_order_items ( id, order_id, name ) AS
SELECT 1, 3, 'MNO_NNN' FROM DUAL UNION ALL
SELECT 2, 3, 'MNO_OOO' FROM DUAL UNION ALL
SELECT 3, 3, 'MNO_MMM' FROM DUAL UNION ALL
SELECT 4, 2, 'ABC_AAA' FROM DUAL;
CREATE TABLE customer_order_item_parts ( id, item_id, name ) AS
SELECT 1, 1, 'Part_2_N' FROM DUAL UNION ALL
SELECT 2, 1, 'Part_1_N' FROM DUAL UNION ALL
SELECT 3, 2, 'Part_1_O' FROM DUAL UNION ALL
SELECT 4, 2, 'Part_3_O' FROM DUAL UNION ALL
SELECT 5, 4, 'Part_5_A' FROM DUAL UNION ALL
SELECT 6, 4, 'Part_3_A' FROM DUAL UNION ALL
SELECT 7, 4, 'Part_2_A' FROM DUAL UNION ALL
SELECT 8, 4, 'Part_4_A' FROM DUAL;
Then you can use UNION ALL (and JOINs as required) to concatenate the data and once it is all compiled then you can apply a hierarchical query:
SELECT *
FROM (
SELECT id AS order_id,
NULL AS item_id,
NULL AS part_id,
name
FROM customer_orders
UNION ALL
SELECT order_id,
id,
NULL,
name
FROM customer_order_items
UNION ALL
SELECT i.order_id,
p.item_id,
p.id,
p.name
FROM customer_order_items i
INNER JOIN
customer_order_item_parts p
ON ( i.id = p.item_id )
)
START WITH item_id IS NULL
CONNECT BY NOCYCLE
PRIOR order_id = order_id
AND ( ( PRIOR item_id IS NULL
AND part_id IS NULL )
OR ( PRIOR part_id IS NULL
AND part_id IS NOT NULL
AND PRIOR item_id = item_id )
)
ORDER SIBLINGS BY name
Which outputs:
ORDER_ID | ITEM_ID | PART_ID | NAME
-------: | ------: | ------: | :-------------
2 | null | null | Cust. Ord. ABC
2 | 4 | null | ABC_AAA
2 | 4 | 7 | Part_2_A
2 | 4 | 6 | Part_3_A
2 | 4 | 8 | Part_4_A
2 | 4 | 5 | Part_5_A
3 | null | null | Cust. Ord. MNO
3 | 3 | null | MNO_MMM
3 | 1 | null | MNO_NNN
3 | 1 | 2 | Part_1_N
3 | 1 | 1 | Part_2_N
3 | 2 | null | MNO_OOO
3 | 2 | 3 | Part_1_O
3 | 2 | 4 | Part_3_O
1 | null | null | Cust. Ord. XYZ
db<>fiddle here