SQL grouping data with overlapping timespans - sql

Question

I need to group data together that are related to each other by overlapping timespans based on the records start and end times. SQL-fiddle here: http://sqlfiddle.com/#!18/87e4b/1/0
The current query I have built is giving incorrect results. Callid 3 should give a callCount of 4. It does not because record 6 is not included since it does not overlap with 3, but should be included because it does overlap with one of the other related records. So I believe a recursive CTE may be in need but I am unsure how to write this.
Schema:
CREATE TABLE Calls
([callid] int, [src] varchar(10), [start] datetime, [end] datetime, [conf] varchar(5));
INSERT INTO Calls
([callid],[src],[start],[end],[conf])
VALUES
('1','5555550001','2019-07-09 10:00:00', '2019-07-09 10:10:00', '111'),
('2','5555550002','2019-07-09 10:00:01', '2019-07-09 10:11:00', '111'),
('3','5555550011','2019-07-09 11:00:00', '2019-07-09 11:10:00', '111'),
('4','5555550012','2019-07-09 11:00:01', '2019-07-09 11:11:00', '111'),
('5','5555550013','2019-07-09 11:01:00', '2019-07-09 11:15:00', '111'),
('6','5555550014','2019-07-09 11:12:00', '2019-07-09 11:16:00', '111'),
('7','5555550014','2019-07-09 15:00:00', '2019-07-09 15:01:00', '111');
Current query:
SELECT
detail_record.callid,
detail_record.conf,
MIN(related_record.start) AS sessionStart,
MAX(related_record.[end]) As sessionEnd,
COUNT(related_record.callid) AS callCount
FROM
Calls AS detail_record
INNER JOIN
Calls AS related_record
ON related_record.conf = detail_record.conf
AND ((related_record.start >= detail_record.start
AND related_record.start < detail_record.[end])
OR (related_record.[end] > detail_record.start
AND related_record.[end] <= detail_record.[end])
OR (related_record.start <= detail_record.start
AND related_record.[end] >= detail_record.[end])
)
WHERE
detail_record.start > '1/1/2019'
AND detail_record.conf = '111'
GROUP BY
detail_record.callid,
detail_record.start,
detail_record.conf
HAVING
MIN(related_record.start) >= detail_record.start
ORDER BY sessionStart DESC
Expected Results:
callid conf sessionStart sessionEnd callCount
7 111 2019-07-09T15:00:00Z 2019-07-09T15:01:00Z 1
3 111 2019-07-09T11:00:00Z 2019-07-09T11:15:00Z 4
1 111 2019-07-09T10:00:00Z 2019-07-09T10:11:00Z 2

Answer 1

This is a gaps-and-islands problem. It does not require a recursive CTE. You can use window functions:
select min(callid), conf, grouping, min([start]), max([end]), count(*)
from (select c.*,
sum(case when prev_end < [start] then 1 else 0 end) over (order by start) as grouping
from (select c.*,
max([end]) over (partition by conf order by [start] rows between unbounded preceding and 1 preceding) as prev_end
from calls c
) c
) c
group by conf, grouping;
The innermost subquery calculates the previous end. The middle subquery compares this to the current start, to determine when groups of adjacent rows are the beginning of a new group. A cumulative sum then determines the grouping.
And, the outer query aggregates to summarize information about each group.
Here is a db<>fiddle.