SQL calculate date segments within calendar year - sql

Question

What I need is to calculate the missing time periods within the calendar year given a table such as this in SQL:
DatesTable
|ID|DateStart |DateEnd |
1 NULL NULL
2 2015-1-1 2015-12-31
3 2015-3-1 2015-12-31
4 2015-1-1 2015-9-30
5 2015-1-1 2015-3-31
5 2015-6-1 2015-12-31
6 2015-3-1 2015-6-30
6 2015-7-1 2015-10-31
Expected return would be:
1 2015-1-1 2015-12-31
3 2015-1-1 2015-2-28
4 2015-10-1 2015-12-31
5 2015-4-1 2015-5-31
6 2015-1-1 2015-2-28
6 2015-11-1 2015-12-31
It's essentially work blocks. What I need to show is the part of the calendar year which was NOT worked. So for ID = 3, he worked from 3/1 through the rest of the year. But he did not work from 1/1 till 2/28. That's what I'm looking for.

Answer 1

You can do it using LEAD, LAG window functions available from SQL Server 2012+:
;WITH CTE AS (
SELECT ID,
LAG(DateEnd) OVER (PARTITION BY ID ORDER BY DateEnd) AS PrevEnd,
DateStart,
DateEnd,
LEAD(DateStart) OVER (PARTITION BY ID ORDER BY DateEnd) AS NextStart
FROM DatesTable
)
SELECT ID, DateStart, DateEnd
FROM (
-- Get interval right before current [DateStart, DateEnd] interval
SELECT ID,
CASE
WHEN DateStart IS NULL THEN '20150101'
WHEN DateStart > start THEN start
ELSE NULL
END AS DateStart,
CASE
WHEN DateStart IS NULL THEN '20151231'
WHEN DateStart > start THEN DATEADD(d, -1, DateStart)
ELSE NULL
END AS DateEnd
FROM CTE
CROSS APPLY (SELECT COALESCE(DATEADD(d, 1, PrevEnd), '20150101')) x(start)
-- If there is no next interval then get interval right after current
-- [DateStart, DateEnd] interval (up-to end of year)
UNION ALL
SELECT ID, DATEADD(d, 1, DateEnd) AS DateStart, '20151231' AS DateEnd
FROM CTE
WHERE DateStart IS NOT NULl -- Do not re-examine [Null, Null] interval
AND NextStart IS NULL -- There is no next [DateStart, DateEnd] interval
AND DateEnd < '20151231' -- Current [DateStart, DateEnd] interval
-- does not terminate on 31/12/2015
) AS t
WHERE t.DateStart IS NOT NULL
ORDER BY ID, DateStart
The idea behind the above query is simple: for every [DateStart, DateEnd] interval get 'not worked' interval right before it. If there is no interval following the current interval, then also get successive 'not worked' interval (if any).
Also note that I assume that if DateStart is NULL then DateStart is also NULL for the same ID.
Demo here

Answer 2

If your data is not too big, this approach will work. It expands all the days and ids and then re-groups them:
with d as (
select cast('2015-01-01' as date)
union all
select dateadd(day, 1, d)
from d
where d < cast('2015-12-31' as date)
),
td as (
select *
from d cross join
(select distinct id from t) t
where not exists (select 1
from t t2
where d.d between t2.startdate and t2.enddate
)
)
select id, min(d) as startdate, max(d) as enddate
from (select td.*,
dateadd(day, - row_number() over (partition by id order by d), d) as grp
from td
) td
group by id, grp
order by id, grp;
An alternative method relies on cumulative sums and similar functionality that is much easier to expression in SQL Server 2012+.

Answer 3

Somewhat simpler approach I think.
Basically create a list of dates for all work block ranges (A). Then create a list of dates for the whole year for each ID (B). Then remove the A from B. Compile the remaining list of dates into date ranges for each ID.
DECLARE #startdate DATETIME, #enddate DATETIME
SET #startdate = '2015-01-01'
SET #enddate = '2015-12-31'
--Build date ranges from remaining date list
;WITH dateRange(ID, dates, Grouping)
AS
(
SELECT dt1.id, dt1.Dates, dt1.Dates + row_number() over (order by dt1.id asc, dt1.Dates desc) AS Grouping
FROM
(
--Remove (A) from (B)
SELECT distinct dt.ID, tmp.Dates FROM DatesTable dt
CROSS APPLY
(
--GET (B) here
SELECT DATEADD(DAY, number, #startdate) [Dates]
FROM master..spt_values
WHERE type = 'P' AND DATEADD(DAY, number, #startdate) <= #enddate
) tmp
left join
(
--GET (A) here
SELECT DISTINCT T.Id,
D.Dates
FROM DatesTable AS T
INNER JOIN master..spt_values as N on N.number between 0 and datediff(day, T.DateStart, T.DateEnd)
CROSS APPLY (select dateadd(day, N.number, T.DateStart)) as D(Dates)
WHERE N.type ='P'
) dr
ON dr.Id = dt.Id and dr.Dates = tmp.Dates
WHERE dr.id is null
) dt1
)
SELECT ID, CAST(MIN(Dates) AS DATE) DateStart, CAST(MAX(Dates) AS DATE) DateEnd
FROM dateRange
GROUP BY ID, Grouping
ORDER BY ID
Heres the code:
http://sqlfiddle.com/#!3/f3615/1
I hope this helps!