Getting distinct rows for overlapping timestamp in SQL Server - sql

Question

I have the following result set which I get from SQL Server:
employeeNumber | start_date | start_time | end_date | end_time
---------------+------------+------------+--------------+----------
123 | 10-03-2020 | 18:13:55 | 10-03-2020 | 22:59:46
123 | 10-03-2020 | 18:24:22 | 10-03-2020 | 22:59:51
123 | 10-03-2020 | 23:24:22 | 10-03-2020 | 23:59:51
123 | 11-03-2020 | 18:25:25 | 11-03-2020 | 20:59:51
123 | 12-03-2020 | 18:40:22 | 12-03-2020 | 22:59:52
For some cases I have multiple rows for the same overlapping time (row 1 and 2) as above but with a different start and end time (difference in seconds or minutes).
While my query is a simple select query that fetches the data from the source table, What can i add in the where clause to fetch distinct rows for such overlapping timestamp rows. i.e. for the above query i would want the result set to return the following :
employeeNumber | start_date | start_time | end_date | end_time
---------------+------------+------------+--------------+----------
123 | 10-03-2020 | 18:13:55 | 10-03-2020 | 22:59:46
123 | 10-03-2020 | 23:24:22 | 10-03-2020 | 23:59:51
123 | 11-03-2020 | 18:25:25 | 11-03-2020 | 20:59:51
123 | 12-03-2020 | 18:40:22 | 12-03-2020 | 22:59:52
Below is my query :
select
employeeNumber, start_date, start_time, end_date, end_time
from
emp_data
where
employeeNumber = 123
order by
employeeNumber;
I can probably do with fetching only the first record but what would the where clause be.
Any help is appreciated as I am not very familiar with SQL Server.

Answer 1

This is complicated. You need to keep track of "starts" and "ends". I am going to assume that your columns are datetimes or something similar that can be combined into a single column:
with e as (
select e.employeeNumber, v.dt, sum(v.inc) as inc,
sum(sum(v.inc)) over (partition by e.employeeNumber order by v.dt) as in_outs
from emp_data e cross apply
(values (start_date + start_time, 1),
(end_date + end_time, -1)
) v(dt, inc)
group by e.employeeNumber, v.dt
)
select employeeNumber, min(dt) as start_datetime, max(dt) as end_datetime
from (select e.*,
sum(case when in_outs = 0 then 1 else 0 end) over (partition by employeeNumber order by dt) as grp
from e
) e
where in_outs <> 0
group by employeeNumber, grp;
Here is a db<>fiddle.
What is this doing?
First the date/times are converted to date times.
Then the columns are unpivoted and identified as starts and ends, along with +1 or -1 to indicate whether the employee is "entering" or "existing" at that time.
These are accumulated.
Now you have a gaps and islands problem, where you want to find continue periods of "in"s. The "islands" are identified using a cumulative sum of "ins".
Then these are aggregated.
EDIT:
You can replace the cumulative sum with:
from (select e.*,
(select sum(case when e2.in_outs = 0 then 1 else 0 end)
from e e2
where e2.employeeNumber = e.employeeNumber
e2.dt <= e.dt
) as grp
from e
) e