select rows in sql with end_date >= start_date for each ID repeated multiple times - sql

Question

Attached the image how the data looks like. In my table I have 3 columns id, start date, and end date, and values like this:
id start date end date
-------------------------------
100 2015-01-01 2015-12-31
100 2016-01-10 2018-12-31
200 2015-02-15 2016-03-15
200 2016-03-15 2016-12-31
300 2016-01-01 2016-12-31
400 2017-01-01 2017-12-31
500 2017-02-01 2017-12-31
600 2017-01-15 2017-03-05
600 2017-02-01 2018-12-31
I want my output to be
id start date end date
--------------------------------
100 2015-01-01 2015-12-31
100 2016-01-10 2018-12-31
200 2015-02-15 2016-12-31
300 2016-01-01 2016-12-31
400 2017-01-01 2017-12-31
500 2017-02-01 2017-12-31
600 2017-01-15 2018-12-31
Query:
select
id, *
from
dbo.test_sl
where
id in (select id
from dbo.test_sl
where end_date >= start_date
group by id)
Please help me get the output I am looking for.

Answer 1

This is an example of a gaps-and-islands problem. In this case, you want to find adjacent rows that do not overlap for the same id. These are the starts of groups. A cumulative sum of the starts of a group providing a grouping number, which can be used for aggregation.
In a query, this looks like:
select id, min(startdate), max(enddate)
from (select t.*,
sum(isstart) over (partition by id order by startdate) as grp
from (select t.*,
(case when exists (select 1
from test_sl t2
where t2.id = t.id and
t2.startdate < t.startdate and
t2.enddate >= t.startdate
)
then 0 else 1
end) as isstart
from test_sl t
) t
) t
group by id, grp;

Answer 2

Assuming that only two records can be combined together, you can LEFT JOIN the table with itself and then use a CASE to display the end date of the self-joined record, if available.
SELECT
t1.id,
min(t1.start_date),
CASE WHEN t2.end_date IS NULL THEN t1.end_date ELSE t2.end_date END
FROM
table t1
LEFT JOIN table t2
ON t1.id = t2.id
AND t2.start_date > t1.start_date
AND t2.start_date <= t1.end_date
GROUP BY
t1.id,
CASE WHEN t2.end_date IS NULL THEN t1.end_date ELSE t2.end_date END
ORDER BY 1
Tested in this SQL Fiddle

Answer 3

Here's a solution that uses a Recursive CTE.
It basically loops through the dates per id, and keeps the smallest start_date for the overlapping end_date/start_date.
Then the result is grouped so there are no more overlaps.
Test here on rextester.
WITH SRC AS
(
SELECT id, start_date, end_date,
row_number() over (partition by id order by start_date) as rn
FROM test_sl
)
, RCTE AS
(
SELECT id, rn, start_date, end_date
FROM SRC
WHERE rn = 1
UNION ALL
SELECT t.id, t.rn, iif(r.end_date >= t.start_date, r.start_date, t.start_date), t.end_date
FROM RCTE r
JOIN SRC t ON t.id = r.id AND t.rn = r.rn + 1
)
SELECT id, start_date, max(end_date) as end_date
FROM RCTE
GROUP BY id, start_date
ORDER BY id, start_date;