Split Overlapping\Merged Dates in SQL - sql

Question

I have a requirement where I will have to split overlapping records on a given table with 2 date fields.
Consider this to be my input table TableT.
ID
EFFECTIVE_DATE
END_DATE
JKL
2016-01-01
2016-12-31
JKL
2016-04-01
2016-12-31
JKL
2016-01-01
2016-03-04
JKL
2016-04-01
2016-12-31
JKL
2016-01-01
2016-12-31
I would want my output to look like below. I need to achieve this in both SQL Server and Oracle\DB2 so I am looking for a generic solution.
ID
EFFECTIVE_DATE
END_DATE
JKL
2016-01-01
2016-03-04
JKL
2016-03-05
2016-03-31
JKL
2016-04-01
2016-12-31
This is what I have tried
With EndDates as (
select END_DATE as END_DATE,TRIM(ID) as ID FROM TableT
union all
select ADD_DAYS(EFFECTIVE_DATE, -1) as END_DATE,TRIM(ID) as ID FROM TableT
), Periods as (
select ID as ID,MIN(EFFECTIVE_DATE) as EFFECTIVE_DATE,
(select MIN(END_DATE) from EndDates e
where e.ID = t.ID and
e.END_DATE >= MIN(EFFECTIVE_DATE)) as END_DATE
from
TableT t
group by ID),
EXTN_PERIOD as (select p.ID as ID, ADD_DAYS(p.END_DATE, 1) as EFFECTIVE_DATE,e.END_DATE as END_DATE
from
Periods p
inner join
EndDates e
on
p.ID = e.ID and
p.END_DATE < e.END_DATE
where
not exists (select * from EndDates e2 where
e2.ID = p.ID and
e2.END_DATE > p.END_DATE and
e2.END_DATE < e.END_DATE)
)
select * from EXTN_PERIOD
union
select * from PERIODS
It works partially fine but does not give me the desired output.
This is what the output I get when I run the above query:
ID
EFFECTIVE_DATE
END_DATE
JKL
2016-01-01
2016-03-04
JKL
2016-03-05
2016-03-31
Thanks in advance!

Answer 1

WITH
/*
MY_TAB (ID, EFFECTIVE_DATE, END_DATE) AS
(
VALUES
('JKL', DATE('2016-01-01'), DATE('2016-12-31'))
, ('JKL', DATE('2016-04-01'), DATE('2016-12-31'))
, ('JKL', DATE('2016-01-01'), DATE('2016-03-04'))
, ('JKL', DATE('2016-04-01'), DATE('2016-12-31'))
, ('JKL', DATE('2016-01-01'), DATE('2016-12-31'))
)
,
*/
A AS
(
SELECT DISTINCT T.ID, DECODE(V.I, 1, T.EFFECTIVE_DATE, 2, T.END_DATE + 1) DT
FROM MY_TAB T, (VALUES 1, 2) V(I)
)
, INTL AS
(
SELECT
ID
, LAG(DT) OVER (PARTITION BY ID ORDER BY DT) AS EFF_DT
, DT AS END_DT
FROM A
)
SELECT ID, EFF_DT, END_DT - 1 AS END_DT
FROM INTL
WHERE EFF_DT IS NOT NULL
ORDER BY 1, 2;
Almost universal. The only customization is the way the "virtual" table with the correlation name V of 2 rows (with INTEGERS 1 and 2) is generated.
The idea is to convert your data first to [inclusive, exclusive) form to simplify further calculations. Then we merge all effective and end dates and construct intervals using the OLAP LAG function. Finally we revert to your [inclusive, inclusive] form.
db<>fiddle link to test.

Answer 2

In Oracle you could do something like this:
with
tablet (id, effective_date, end_date) as (
select 'JKL', date '2016-01-01', date '2016-12-31' from dual union all
select 'JKL', date '2016-04-01', date '2016-12-31' from dual union all
select 'JKL', date '2016-01-01', date '2016-03-04' from dual union all
select 'JKL', date '2016-04-01', date '2016-12-31' from dual union all
select 'JKL', date '2016-01-01', date '2016-12-31' from dual
)
, prep (id, dt) as (
select distinct id, case col when 'EFF' then val else val + 1 end
from tablet
unpivot (val for col in (effective_date as 'EFF', end_date as 'END'))
)
, almost_done (id, effective_date, end_date) as (
select id, dt, lead(dt) over (partition by id order by dt) - 1
from prep
)
select id, effective_date, end_date
from almost_done
where end_date is not null
;
ID EFFECTIVE_DATE END_DATE
--- -------------- ----------
JKL 2016-01-01 2016-03-04
JKL 2016-03-05 2016-03-31
JKL 2016-04-01 2016-12-31
Notice the first CTE (tablet, used to generate testing data - you don't need it in your real-life case). Then, the first step is to unpivot the data; I don't know how SQL Server supports unpivoting, worst case you can do it manually with a cross join. (NOT with UNION ALL - that is inefficient.) Then you remove duplicates, and the rest is easy with the LEAD analytic function, which SQL Server should support too.