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.
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
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