Oracle SQL - Find origin ID of autoincrement column - sql

Question

There's a table on my ERP database that has data about certain events. It has the start date, end date and a column shows if the event is a continuation of a previous one (sequential_id references unique_id). Here's an example:
unique_id
start_date
end_date
sequential_id
001
2021-01-01
2021-01-15
002
2021-02-01
2021-02-16
001
003
2021-03-01
2021-03-17
002
004
2021-03-10
2021-03-11
005
2021-03-19
In the example above, rows 001, 002 and 003 are all part of the same event, and 004/005 are unique events, with no sequences. How can I group the data in a way that the output is like this:
origin_id
start_date
end_date
001
2021-01-01
2021-03-17
004
2021-03-10
2021-03-11
005
2021-03-19
I've tried using group by, but due to sequential_id being auto incremental, it didn't work.
Thanks in advance.

Answer 1

You can use modern match_recognize which is an optimal solution for such tasks:
Pattern Recognition With MATCH_RECOGNIZE
DBFiddle
select *
from t
match_recognize(
measures
first(unique_id) start_unique_id,
first(start_date) start_date,
last(end_date) end_date
pattern (strt nxt*)
define nxt as sequential_id=prev(unique_id)
);

Answer 2

You can use hierarchical query for this:
with a (unique_id, start_date, end_date, sequential_id) as (
select '001', date '2021-01-01', date '2021-01-15', null from dual union all
select '002', date '2021-02-01', date '2021-02-16', '001' from dual union all
select '003', date '2021-03-01', date '2021-03-17', '002' from dual union all
select '004', date '2021-03-10', date '2021-03-11', null from dual union all
select '005', date '2021-03-19', null, null from dual
)
, b as (
select
connect_by_root(unique_id) as unique_id
, connect_by_root(start_date) as start_date
, end_date
, connect_by_isleaf as l
from a
start with sequential_id is null
connect by prior unique_id = sequential_id
)
select
unique_id
, start_date
, end_date
from b
where l = 1
order by 1 asc
UNIQUE_ID | START_DATE | END_DATE
:-------- | :--------- | :--------
001 | 01-JAN-21 | 17-MAR-21
004 | 10-MAR-21 | 11-MAR-21
005 | 19-MAR-21 | null
db<>fiddle here

Answer 3

This is a graph-walking problem, so you can use a recursive CTE:
with cte (unique_id, start_date, end_date, start_unique_id) as (
select unique_id, start_date, end_date, unique_id
from t
where not exists (select 1 from t t2 where t.sequential_id = t2.unique_id)
union all
select t.unique_id, t.start_date, t.end_date, cte.start_unique_id
from cte join
t
on cte.unique_id = t.sequential_id
)
select start_unique_id, min(start_date), max(end_date)
from cte
group by start_Unique_id;
Here is a db<>fiddle.