I need to handle overlapping dates but if the end date is null then it to be assumed that the process has not stopped - sql

Question

I have a start date and end date of a process from two different sources.these two sources will be merged and the dates needs to be handled in case of conflicts
Dataset1
P_startDate P_EndDate
1-Jan-07 1-Jun-15
Dataset2
P_Start Date P_End Date
1-Mar-15 1-Jan-17
2-Jan-17 Null
Merged Dataset / Expected Dataset
| Process Start Date | Process End Date |
| 1-Jan-07 | 1-Mar-15 |
| 1-Mar-15 | 1-Jan-17 |
| 2-Jan-17 | Null |
I did create a code but that is giving me a result where the null (no end date) condition is not considered and my out put comes as
| Process Start Date | Process End Date |
| 1-Jan-07 | 1-Mar-15 |
| 1-Mar-15 | 1-Jan-17 |
| 1-Jan-17 | 2-Jan-17 |
I have followed the guidelines from here
http://www.schemamania.org/sql/#overlapping.dates
with D (ID, bound) as (
select ID
, case T when 's' then StartDate else EndDate end as bound
from (
select ID, StartDate, EndDate from so.A
UNION
select ID, StartDate, EndDate from so.B
) as U
cross join (select 's' as T union select 'e') as T
)
select P.*
from (
select s.ID, s.bound as StartDate, min(e.bound) as EndDate
from D as s join D as e
on s.ID = e.ID
and s.bound < e.bound
group by s.ID, s.bound
) as P
left join so.A as a
on P.ID = a.ID
and a.StartDate <= P.StartDate and P.EndDate <= a.EndDate
left join so.B as b
on P.ID = b.ID
and b.StartDate <= P.StartDate and P.EndDate <= b.EndDate
order by P.ID, P.StartDate, P.EndDate

Answer 1

This looks more like a merge overlapping interval problem. Here is one solution that keeps a running count of starts and ends:
CREATE TABLE ds1 (P_STARTDATE DATE, P_ENDDATE DATE);
CREATE TABLE ds2 (P_STARTDATE DATE, P_ENDDATE DATE);
INSERT INTO ds1 VALUES
('2007-01-01', '2015-06-01');
INSERT INTO ds2 VALUES
('2015-03-01', '2017-01-01'),
('2017-01-02', NULL);
WITH cte1(d, v) AS (
SELECT P_startDate, +1 FROM ds1 UNION ALL
SELECT P_EndDate, -1 FROM ds1 UNION ALL
SELECT P_startDate, +1 FROM ds2 UNION ALL
SELECT P_EndDate, -1 FROM ds2
), cte2(d, c) AS (
SELECT d, SUM(SUM(v)) OVER (ORDER BY CASE WHEN d IS NULL THEN 2 ELSE 1 END, d)
FROM cte1
GROUP BY d
), cte3(d, c, f) AS (
SELECT d, c, CASE WHEN LAG(c) OVER (ORDER BY CASE WHEN d IS NULL THEN 2 ELSE 1 END, d) > 0 THEN 0 ELSE 1 END
FROM cte2
), cte4(d, c, g) AS (
SELECT d, c, SUM(f) OVER (ORDER BY CASE WHEN d IS NULL THEN 2 ELSE 1 END, d)
FROM cte3
)
SELECT MIN(d) AS FromDate, CASE WHEN COUNT(d) = COUNT(*) THEN MAX(d) END AS ToDate
FROM cte4
GROUP BY g;
Result:
FromDate ToDate
01/01/2007 00:00:00 01/01/2017 00:00:00
02/01/2017 00:00:00 02/01/2017 00:00:00