Hierarchical query find all parents with some filters - oracle

Question

I've a structure like:
CREATE TABLE BUSINESS_UNIT (
ID NUMBER,
DESCPRIPTION VARCHAR2(100 CHAR),
TAG VARCHAR2(10 CHAR)
);
CREATE TABLE USERS (
ID NUMBER,
LOGIN VARCHAR2(10 CHAR)
);
CREATE TABLE BU_USERS (
ID_BU NUMBER,
ID_USER NUMBER
);
CREATE TABLE BU_TREE (
ID_BU NUMBER,
ID_PARENT NUMBER
);
INSERT INTO BUSINESS_UNIT VALUES(1, 'ONE', 'WHITE');
INSERT INTO BUSINESS_UNIT VALUES(2, 'TWO', 'RED');
INSERT INTO BUSINESS_UNIT VALUES(3, 'THREE', 'YELLOW');
INSERT INTO BUSINESS_UNIT VALUES(4, 'FOUR', 'GREEN');
INSERT INTO BUSINESS_UNIT VALUES(5, 'FIVE', 'GREEN');
INSERT INTO BUSINESS_UNIT VALUES(6, 'SIX', 'RED');
INSERT INTO BUSINESS_UNIT VALUES(7, 'SEVEN', 'GREEN');
INSERT INTO USERS VALUES(1, 'USER1');
INSERT INTO BU_USERS VALUES(5, 1);
/*
___1w___
___2r___ 3y___
__4g 7g 6r
5g
*/
INSERT INTO BU_TREE VALUES(5, 4);
INSERT INTO BU_TREE VALUES(4, 2);
INSERT INTO BU_TREE VALUES(7, 2);
INSERT INTO BU_TREE VALUES(2, 1);
INSERT INTO BU_TREE VALUES(3, 1);
INSERT INTO BU_TREE VALUES(6, 3);
And I have to get parent record with TAG = "RED".
I tried something like:
SELECT
B.ID
FROM BUSINESS_UNIT B
INNER JOIN BU_TREE T ON (B.ID = T.ID_BU)
START WITH B.ID = (SELECT ID_BU FROM BU_USERS WHERE ID_USER = 1)
CONNECT BY PRIOR B.ID = T.ID_PARENT
But it returns only the "directly" father, that is the 5.
So, for the user one I have to get its parent red business unit: the number two.
Why my query doesn't returns all the parents?
Thanks

Answer 1

Why my query doesn't returns all the parents?
Well, it does return all the parents.
But there is no any parents that meet the condition CONNECT BY PRIOR B.ID = T.ID_PARENT, so the query shows only 1 record.
Please look at the below query, it shows the whole resultset of the join:
SELECT *
FROM BUSINESS_UNIT B
inner JOIN BU_TREE T ON (B.ID = T.ID_BU);
ID DESCPRIPTI TAG ID_BU ID_PARENT
---------- ---------- ---------- ---------- ----------
2 TWO RED 2 1
3 THREE YELLOW 3 1
4 FOUR GREEN 4 2
5 FIVE GREEN 5 4
6 SIX RED 6 3
7 SEVEN GREEN 7 2
The subquery (SELECT ID_BU FROM BU_USERS WHERE ID_USER = 1) gives 5, so your query is equivalent to:
SELECT *
FROM BUSINESS_UNIT B
inner JOIN BU_TREE T ON (B.ID = T.ID_BU);
START WITH B.ID = 5
CONNECT BY PRIOR B.ID = T.ID_PARENT;
WHen running this query, in the frst step Oracle evaluates START WITH B.ID = 5 conditions, and picks rows that meet this condition, that is:
ID DESCPRIPTI TAG ID_BU ID_PARENT
---------- ---------- ---------- ---------- ----------
5 FIVE GREEN 5 4
In the next step, oracle applies CONNECT BY PRIOR B.ID = T.ID_PARENT; condition to the above "prior" record (taking PRIOR ID = 5 from this record), and then search for records that meet the right side of the condition (5 = ID_PARENT) in the resultset of join.
There is no any record with parent_id = 5 in the result of join, so the final result of the connect-by query is:
ID ID_BU ID_PARENT
---------- ---------- ----------
5 5 4