Managing dates when they're overlapping - oracle

Question

How to write a procedure so that when adding a new insert, rows are added appropriately?
Let's say i have a table:
create table test_table
(
code varchar2(10) not null,
type varchar2(50) not null,
start_date date not null,
end_date date not null,
parameter number
);
1. First test case:
In table we have:
insert into test_table values ('CODE', 'a', to_date('01.01.2021', 'DD,MM,YYYY'), to_date('10.01.2021', 'DD,MM,YYYY'), 1);
[2021-01-01 - 2021-01-10] type = "a" parameter = 1
and when we want to insert:
insert into test_table values ('CODE', 'a', to_date('01.01.2021', 'DD,MM,YYYY'), to_date('20.01.2021', 'DD,MM,YYYY'), 1)
[2021-01-11 - 2021-01-20] type = "a" parameter = 1
*Result should be:
2021-01-01 - 2021-01-20 type = "a" parameter = 1*
2. Second test case:
In table we have:
insert into test_table values ('CODE', 'a', to_date('01.01.2021', 'DD,MM,YYYY'), to_date('10.01.2021', 'DD,MM,YYYY'), 1)
[2021-01-01 - 2021-01-10] type = "a" parameter = 1
and when we want to insert:
insert into test_table values ('CODE', 'a', to_date('06.01.2021', 'DD,MM,YYYY'), to_date('20.01.2021', 'DD,MM,YYYY'), 2)
[2021-01-06 - 2021-01-20] type = "a" parameter = 2
*in result we should have:
[2021-01-01 - 2021-01-05] type = "a" parameter = 1
[2021-01-06 - 2021-01-20] type = "a" parameter = 2*
3. Third test case:
In table we have:
insert into test_table values ('CODE', 'a', to_date('01.01.2021', 'DD,MM,YYYY'), to_date('10.01.2021', 'DD,MM,YYYY'), 1)
[2021-01-01 - 2021-01-20] type = "a" parameter = 1
and when we want to insert:
insert into test_table values ('CODE', 'a', to_date('06.01.2021', 'DD,MM,YYYY'), to_date('15.01.2021', 'DD,MM,YYYY'), 2)
[2021-01-06 - 2021-01-15] type = "a" parameter = 2
*in result we should have:
[2021-01-01 - 2021-01-05] type = "a" parameter = 1
[2021-01-06 - 2021-01-15] type = "a" parameter = 2
[2021-01-16 - 2021-01-20] type = "a" parameter = 1*

Answer 1

When you insert a new date range that is completely contained in the middle of an existing date range then you need to: INSERT of the new range; UPDATE the existing range to the portion of that range before the new range; and INSERT a new range for the portion of the existing range after the new range. So you need a total of 3 changes.
Similarly, when you insert a new date range that completely contains an existing range then you need to: INSERT the new range; and DELETE the existing range (or do a single UPDATE statement).
You can use a single MERGE statement for all of these actions:
MERGE INTO test_table dst
USING (
WITH new_data (code, type, start_date, end_date, parameter) AS (
SELECT 'CODE2', 'a', DATE '2021-01-01', DATE '2021-01-20', 2 FROM DUAL
)
SELECT NULL AS rid,
n.*,
0 AS status -- Insert
FROM new_data n
UNION ALL
-- Existing rows overlapping before
SELECT t.ROWID,
t.code,
t.type,
t.start_date,
n.start_date - INTERVAL '1' DAY,
t.parameter,
1 -- Update overlap before
FROM test_table t
INNER JOIN new_data n
ON ( t.start_date <= n.start_date
AND t.end_date >= n.start_date)
UNION ALL
SELECT t.ROWID,
t.code,
t.type,
n.end_date + INTERVAL '1' DAY,
t.end_date,
t.parameter,
CASE
WHEN n.start_date <= t.end_date AND t.end_date <= n.end_date
THEN 2 -- Delete
WHEN t.start_date < n.start_date AND n.end_date < t.end_date
THEN 0 -- Insert overlap afterwards
ELSE 1 -- Update overlap afterwards
END
FROM test_table t
INNER JOIN new_data n
ON ( t.start_date <= n.end_date
AND t.end_date >= n.start_date)
WHERE NOT (t.start_date <= n.start_date AND t.end_date <= n.end_date)
) src
ON (src.rid = dst.ROWID AND status > 0)
WHEN MATCHED THEN
UPDATE
SET code = src.code,
start_date = src.start_date,
end_date = src.end_date
DELETE
WHERE status = 2
OR src.start_date > src.end_date
WHEN NOT MATCHED THEN
INSERT (code, type, start_date, end_date, parameter)
VALUES (src.code, src.type, src.start_date, src.end_date, src.parameter);
db<>fiddle here