Find the date when a milestone was achieved - sql-server

Question

I have people that do many multi-day assignments (date x to date Y). I would like to find the date that they completed a milestone e.g. 50 days work completed.
Data is stored as a single row per Assignment
AssignmentId
StartDate
EndDate
I can sum up the total days they have completed up to a date, but am struggling to see how I would find out the date that a milestone was hit. e.g. How many people completed 50 days in October 2020 showing the date within the month that this occurred?
Thanks in advance
PS. Our database is SQL Server.

Answer 1

As mentioned by prwvious comments, it would be much easier to help you if you could provide example data and table structure in order help you answer this question.
However, guessing a simple DB structure with a table for your peolple, your tasks and the work each user completed, you can get the required sum of days by use of a date table (or cte) which contains a entry for each day and the window function SUM with UNBOUNDED PRECEDING. Following an example:
DECLARE #people TABLE(
id int
,name nvarchar(50)
)
DECLARE #tasks TABLE(
id int
,name nvarchar(50)
)
DECLARE #work TABLE(
people_id int
,task_id int
,task_StartDate date
,task_EndDate date
)
INSERT INTO #people VALUES (1, 'Peter'), (2, 'Paul'), (3, 'Mary');
INSERT INTO #tasks VALUES (1, 'Devleopment'), (2, 'QA'), (3, 'Sales');
INSERT INTO #work VALUES
(1, 1, '2019-04-05', '2019-04-08')
,(1, 1, '2019-05-05', '2019-06-08')
,(1, 1, '2019-07-05', '2019-09-08')
,(2, 2, '2019-04-08', '2019-06-08')
,(2, 2, '2019-09-08', '2019-10-03')
,(3, 1, '2019-11-01', '2019-12-01')
;WITH cte AS(
SELECT CAST('2019-01-01' AS DATE) AS dateday
UNION ALL
SELECT DATEADD(d, 1, dateday)
FROM cte
WHERE DATEADD(d, 1, dateday) < '2020-01-01'
),
cteWorkDays AS(
SELECT people_id, task_id, dateday, 1 AS cnt
FROM #work w
INNER JOIN cte c ON c.dateday BETWEEN w.task_StartDate AND w.task_EndDate
),
ctePeopleWorkdays AS(
SELECT *, SUM(cnt) OVER (PARTITION BY people_id ORDER BY dateday ROWS UNBOUNDED PRECEDING) dayCnt
FROM cteWorkDays
)
SELECT *
FROM ctePeopleWorkdays
WHERE dayCnt = 50
OPTION (MAXRECURSION 0)

Answer 2

The solution depends on how you store your data. The solution below assumes that each worked day exists as a single row in your data model.
The approach below uses a common table expression (cte) to generate a running total (Total) for each person (PersonId) and then filters on the milestone target (I set it to 5 to reduce the sample data size) and target month.
Sample data
create table WorkedDays
(
PersonId int,
TaskDate date
);
insert into WorkedDays (PersonId, TaskDate) values
(100, '2020-09-01'),
(100, '2020-09-02'),
(100, '2020-09-03'),
(100, '2020-09-04'),
(100, '2020-09-05'), -- person 100 worked 5 days by 2020-09-05 = milestone (in september)
(200, '2020-09-29'),
(200, '2020-09-30'),
(200, '2020-10-01'),
(200, '2020-10-02'),
(200, '2020-10-03'), -- person 200 worked 5 days by 2020-10-03 = milestone (in october)
(200, '2020-10-04'),
(200, '2020-10-05'),
(200, '2020-10-06'),
(300, '2020-10-10'),
(300, '2020-10-11'),
(300, '2020-10-12'),
(300, '2020-10-13'),
(300, '2020-10-14'), -- person 300 worked 5 days by 2020-10-14 = milestone (in october)
(300, '2020-10-15'),
(400, '2020-10-20'),
(400, '2020-10-21'); -- person 400 did not reach the milestone yet
Solution
with cte as
(
select wd.PersonId,
wd.TaskDate,
count(1) over(partition by wd.PersonId
order by wd.TaskDate
rows between unbounded preceding and current row) as Total
from WorkedDays wd
)
select cte.PersonId,
cte.TaskDate as MileStoneDate
from cte
where cte.Total = 5 -- milestone reached
and year(cte.TaskDate) = 2020
and month(cte.TaskDate) = 10; -- in october
Result
PersonId MilestoneDate
-------- -------------
200 2020-10-03
300 2020-10-14
Fiddle (also shows the common table expression output).