Oracle Hierarchical Queries - oracle

Question

I am struggling with a query with the below requirement:
Table A
ID Name Key
1 A1 Key1
2 A2 Key2
3 A3 Key3
Table B
ID A_ID NAME CONTAINER_A_ID
1 1 B1 NULL
2 1 B2 NULL
3 1 B3 2
4 2 B4 NULL
5 2 B5 NULL
6 3 B6 NULL
7 3 B7 NULL
The Key column in table A is unique
The A_ID column in table B is a foreign key of table A
The CONTAINER_A_ID column in table B means the row in table B can be a
container, it contains other data rows indicated by the CONTAINER_A_ID value.
Below is the example:
the input parameter is table A key column value, let's say A.Key = 'key1', and the result based on the above sample data will be:
A.ID A.NAME A.KEY B.ID B.A_ID B.NAME B.CONTAINER_A_ID
1 A1 KEY1 1 1 B1 NULL
1 A1 KEY1 2 1 B2 NULL
1 A1 KEY1 3 1 B3 2
2 A2 KEY2 4 2 B4 NULL
2 A2 KEY2 5 2 B5 NULL
if the input parameter is A.Key = 'key2', then the result will be:
A.ID A.NAME A.KEY B.ID B.A_ID B.NAME B.CONTAINER_A_ID
2 A2 KEY2 4 2 B4 NULL
2 A2 KEY2 5 2 B5 NULL
Thanks

Answer 1

This is on Oracle 11g.
If you are specifically looking for CONNECT BY I am not aware of that yet.
drop table t1; drop table t2;
create table t1 (id int primary key, name char(5), key char(5));
create table t2 (id int primary key, a_id int, name char(5) , container int);
insert into t1 values (1, 'A1', 'K1');
insert into t1 values (2, 'A2', 'K2');
insert into t1 values (3, 'A3', 'K3');
insert into t2 values (1, 1, 'B1', null);
insert into t2 values (2, 1, 'B2', null);
insert into t2 values (3, 1, 'B3', 2);
insert into t2 values (4, 2, 'B4', null);
insert into t2 values (5, 2, 'B5', null);
insert into t2 values (6, 3, 'B6', null);
insert into t2 values (7, 3, 'B7', null);
with t(id, name, key, bid, aid, bname, con) as (
select a.id, a.name, a.key, b.id, b.a_id, b.name, b.container
from t1 a
inner join
t2 b
on a.id = b.a_id
where a.key = 'K1'
union all
select a.id, a.name, a.key, b.id, b.a_id, b.name, b.container
from t t
inner join
t1 a
on a.id = t.con
inner join
t2 b
on a.id = b.a_id
) select * from t;
EDIT: Reponse to Jorge's comment
insert into t2 values (4, 2, 'B4', 3);

Answer 2

This is for Hierarchical Query
with TableA as
(
select 1 id, 'A1' Name, 'Key1' key from dual union all
select 2, 'A2', 'Key2' from dual union all
select 3, 'A3', 'Key3' from dual
)
, tableb as
(
select 1 id, 1 a_id, 'B1' name , null CONTAINER_A_ID from dual union all
select 2 , 1 , 'B2' , null from dual union all
select 3 , 1 , 'B3' , 2 from dual union all
select 4 , 2 , 'B4' , null from dual union all
select 5 , 2 , 'B5' , null from dual union all
select 6 , 3 , 'B6' , null from dual union all
select 7 , 3 , 'B7' , null from dual
)
select
a.id, a.name, a.key, b.id, b.a_id, b.name, b.container_a_id
from
tableb b
left join
tablea a
on
a.id = b.a_id
start with
A.Key = 'Key1'
connect by
prior b.container_a_id = b.a_id;
If you need order then add order by a.id, b.id,a.name,...; to the end.

Answer 3

CTEs are fine to use in 11g Oracle. I just saw Jorge is in before me. It is easier to see how the recursion works if you just use tableB in the CTE and then join to the CTE to get all the fields, like this
with
recurse (a_id, b_id, parent_id)
as
(select a_id, id, container_a_id as parent_id
from tableB
WHERE A_ID = 1 -- Put your parameter here
union all
select b.a_id, b.id, b.container_a_id
from recurse r, tableB b
where b.a_id = r.parent_id
)
select r.a_id, a.name, a.key, b.id, b.a_id, b.name, b.container_a_id
from recurse r, tableA a, tableB b
where r.a_id = a.id and r.b_id = b.id
;
This gets the same results, but although you have to use a_id and not a_key for the condition, it is a little bit easier to understand the recursion.
So, leaving this here in case it helps someone to understand a bit about CTEs.