Hierarchical query from two different tables in oracle sql - sql

Question

I have a table that contains data something like this
TABLE_A
ID PARENT_ID NAME PROJECT_ID
1 abc
2 1 def
3 2 ghi
4 3 jkl 101
5 1 mno
and I have another table that contains some data that depends on first table 'project_id' :
TABLE_B
ID PROJECT_ID NAME
1 101 prs
2 101 tuv
3 102 xyz
4 102 hgf
I want a result something like this ;
abc
def
ghi
jkl
prs
tuv
mno
I have tried something like this but I did not know how to connect 'TABLE_B'
SELECT LEVEL, A.NAME
FROM TABLE_A A
CONNECT BY PRIOR A.ID = PRIOR A.PARENT_ID
ORDER BY LEVEL;

Answer 1

If I understand well your need, this could be a way:
/* building a test case */
with TABLE_A(ID, PARENT_ID, NAME, PROJECT_ID) as (
select 1, null, 'abc', null from dual union all
select 2, 1 , 'def', null from dual union all
select 3, 2 , 'ghi', null from dual union all
select 4, 3 , 'jkl', 101 from dual union all
select 5, 1 , 'mno', null from dual
),TABLE_B(ID, PROJECT_ID, NAME) as (
select 1, 101, 'prs' from dual union all
select 2, 101, 'tuv' from dual union all
select 3, 102, 'xyz' from dual union all
select 4, 102, 'hgf' from dual
)
/* the query */
select name
from (
select ID, PARENT_ID, NAME, PROJECT_ID
from table_a
UNION ALL
select a.ID, a.PARENT_ID, b.NAME, a.PROJECT_ID
from table_b b
inner join table_a a
on a.project_id = b.project_id
)
start with parent_id is null
connect by prior id = parent_id
The idea here is to build a partial result that contains all the data from table_a and table_b and then use this result in a hierarchical query as if it was a single table.
The result:
abc
def
ghi
jkl
prs
tuv
mno