How to merge time intervals in SQL Server - sql

Question

Suppose I have the following an event table with personId, startDate and endDate.
I want to know how much time the person X spent doing an event (the events can override each other).
If the person just has 1 event, its easy: datediff(dd, startDate, endDate)
If the person has 2 events it gets tricky.
I'll set some scenarios for the expected results.
Scenario 1
startDate endDate
1 4
3 5
This means he the results should be the datediff from 1 to 5
Scenario 2
startDate endDate
1 3
6 9
this means he the results should be the some of datediff(dd,1,3) and datediff(dd,6,9)
How can I get this result on an sql query? I can only think of a bunch of if statements, but the same person can have n events so the query will be really confusing.
Shredder Edit: I'd like to add a 3rd scenario:
startDate endDate
1 5
4 8
11 15
Desired result to Shredder scenario:
(1,5) and (4,8) merge in (1,8) since they overlap then we need to datediff(1,8) + datediff(11,15) => 7 + 4 => 11

Answer 1

You can use a recursive CTE to build a list of dates and then count the distinct dates.
declare #T table
(
startDate date,
endDate date
);
insert into #T values
('2011-01-01', '2011-01-05'),
('2011-01-04', '2011-01-08'),
('2011-01-11', '2011-01-15');
with C as
(
select startDate,
endDate
from #T
union all
select dateadd(day, 1, startDate),
endDate
from C
where dateadd(day, 1, startDate) < endDate
)
select count(distinct startDate) as DayCount
from C
option (MAXRECURSION 0)
Result:
DayCount
-----------
11
Or you can use a numbers table. Here I use master..spt_values:
declare #MinStartDate date
select #MinStartDate = min(startDate)
from #T
select count(distinct N.number)
from #T as T
inner join master..spt_values as N
on dateadd(day, N.Number, #MinStartDate) between T.startDate and dateadd(day, -1, T.endDate)
where N.type = 'P'

Answer 2

Here's a solution that uses the Tally table idea (which I first heard of in an article by Itzk Ben-Gan -- I still cut and paste his code whenver the subject comes up). The idea is to generate a list of ascending integers, join the source data by range against the numbers, and then count the number of distinct numbers, as follows. (This code uses syntax from SQL Server 2008, but with minor modifications would work in SQL 2005.)
First set up some testing data:
CREATE TABLE #EventTable
(
PersonId int not null
,startDate datetime not null
,endDate datetime not null
)
INSERT #EventTable
values (1, 'Jan 1, 2011', 'Jan 4, 2011')
,(1, 'Jan 3, 2011', 'Jan 5, 2011')
,(2, 'Jan 1, 2011', 'Jan 3, 2011')
,(2, 'Jan 6, 2011', 'Jan 9, 2011')
Determine some initial values
DECLARE
#Interval bigint
,#FirstDay datetime
,#PersonId int = 1 -- (or whatever)
Get the first day and the maximum possible number of dates (to keep the cte from generating extra values):
SELECT
#Interval = datediff(dd, min(startDate), max(endDate)) + 1
,#FirstDay = min(startDate)
from #EventTable
where PersonId = #PersonId
Cut and paste over the one routine and modify and test it to only return as many integers as we'll need:
/*
;WITH
Pass0 as (select 1 as C union all select 1), --2 rows
Pass1 as (select 1 as C from Pass0 as A, Pass0 as B),--4 rows
Pass2 as (select 1 as C from Pass1 as A, Pass1 as B),--16 rows
Pass3 as (select 1 as C from Pass2 as A, Pass2 as B),--256 rows
Pass4 as (select 1 as C from Pass3 as A, Pass3 as B),--65536 rows
Pass5 as (select 1 as C from Pass4 as A, Pass4 as B),--4,294,967,296 rows
Tally as (select row_number() over(order by C) as Number from Pass5)
select Number from Tally where Number <= #Interval
*/
And now revise it by first joining to the intervals defined in each source row, and then count each distinct value found:
;WITH
Pass0 as (select 1 as C union all select 1), --2 rows
Pass1 as (select 1 as C from Pass0 as A, Pass0 as B),--4 rows
Pass2 as (select 1 as C from Pass1 as A, Pass1 as B),--16 rows
Pass3 as (select 1 as C from Pass2 as A, Pass2 as B),--256 rows
Pass4 as (select 1 as C from Pass3 as A, Pass3 as B),--65536 rows
Pass5 as (select 1 as C from Pass4 as A, Pass4 as B),--4,294,967,296 rows
Tally as (select row_number() over(order by C) as Number from Pass5)
SELECT PersonId, count(distinct Number) EventDays
from #EventTable et
inner join Tally
on dateadd(dd, Tally.Number - 1, #FirstDay) between et.startDate and et.endDate
where et.PersonId = #PersonId
and Number <= #Interval
group by PersonId
Take out the #PersonId filter and you'd get it for all persons. And with minor modification you can do it for any time interval, not just days (which is why I set the Tally table to generate severely large numbers.)

Answer 3

The following SQL is for the three scenarios you've described
with sampleData
AS (
SELECT 1 personid,1 startDate,4 endDate
UNION SELECT 1,3,5
UNION SELECT 2,1,3
UNION SELECT 2,6,9
UNION SELECT 3,1,5
UNION SELECT 3,4,8
UNION SELECT 3,11, 15
),
cte
AS (SELECT personid,
startdate,
enddate,
Row_number() OVER(ORDER BY personid, startdate) AS rn
FROM sampledata),
overlaps
AS (SELECT a.personid,
a.startdate,
b.enddate,
a.rn id1,
b.rn id2
FROM cte a
INNER JOIN cte b
ON a.personid = b.personid
AND a.enddate > b.startdate
AND a.rn = b.rn - 1),
nooverlaps
AS (SELECT a.personid,
a.startdate,
a.enddate
FROM cte a
LEFT JOIN overlaps b
ON a.rn = b.id1
OR a.rn = b.id2
WHERE b.id1 IS NULL)
SELECT personid,
SUM(timespent) timespent
FROM (SELECT personid,
enddate - startdate timespent
FROM nooverlaps
UNION
SELECT personid,
enddate - startdate
FROM overlaps) t
GROUP BY personid
Produces this result
Personid timeSpent
----------- -----------
1 4
2 5
3 11
Notes: I used the simple integers but the DateDiffs should work too
Correctness issue There is a correctness issue if your data is allowed to have multiple overlaps as Cheran S noted, the results won't be correct and you should use one of the other answers instead. His example used [1,5],[4,8],[7,11] for the same person ID

Answer 4

Algebra. If B-n is the ending time of the nth event, and A-n is the starting time of the nth event, then the sum of the differences is the difference of the sums. So you can write
select everything else, sum(cast(endDate as int)) - sum(cast(startDate as int)) as daysSpent
If your dates have no time component, this works. Otherwise, you could use a real.

Answer 5

Try something like this
select
personId,
sum(DateDuration) as TotalDuration
from
(
select personId, datediff(dd, startDate, endDate) as DateDuration
from yourEventTable
) a
group by personId

Answer 6

;WITH cte(gap)
AS
(
SELECT sum(b-a) from xxx GROUP BY uid
)
SELECT * FROM cte

Answer 7

Edit 1: I have modified both solutions to get correct results.
Edit 2: I have done comparative tests using the solutions proposed by Mikael Eriksson, Conrad Frix, Philip Kelley and me. All tests use an EventTable with the following structure:
CREATE TABLE EventTable
(
EventID INT IDENTITY PRIMARY KEY
,PersonId INT NOT NULL
,StartDate DATETIME NOT NULL
,EndDate DATETIME NOT NULL
,CONSTRAINT CK_StartDate_Before_EndDate CHECK(StartDate < EndDate)
);
Also, all tests use warm buffer (no DBCC DROPCLEANBUFFERS) and cold [plan] cache (I have executed DBCC FREEPROCCACHE before every test). Because some solutions use a filter(PersonId = 1) and others not, I have inserted into EventTable rows for only one person (INSERT ...(PersonId,...) VALUES (1,...)).
These are the results:
My solutions use recursive CTEs.
Solution 1:
WITH BaseCTE
AS
(
SELECT e.StartDate
,e.EndDate
,e.PersonId
,ROW_NUMBER() OVER(PARTITION BY e.PersonId ORDER BY e.StartDate, e.EndDate) RowNumber
FROM EventTable e
), RecursiveCTE
AS
(
SELECT b.PersonId
,b.RowNumber
,b.StartDate
,b.EndDate
,b.EndDate AS MaxEndDate
,1 AS PseudoDenseRank
FROM BaseCTE b
WHERE b.RowNumber = 1
UNION ALL
SELECT crt.PersonId
,crt.RowNumber
,crt.StartDate
,crt.EndDate
,CASE WHEN crt.EndDate > prev.MaxEndDate THEN crt.EndDate ELSE prev.MaxEndDate END
,CASE WHEN crt.StartDate <= prev.MaxEndDate THEN prev.PseudoDenseRank ELSE prev.PseudoDenseRank + 1 END
FROM RecursiveCTE prev
INNER JOIN BaseCTE crt ON prev.PersonId = crt.PersonId
AND prev.RowNumber + 1 = crt.RowNumber
), SumDaysPerPersonAndInterval
AS
(
SELECT src.PersonId
,src.PseudoDenseRank --Interval ID
,DATEDIFF(DAY, MIN(src.StartDate), MAX(src.EndDate)) Days
FROM RecursiveCTE src
GROUP BY src.PersonId, src.PseudoDenseRank
)
SELECT x.PersonId, SUM( x.Days ) DaysPerPerson
FROM SumDaysPerPersonAndInterval x
GROUP BY x.PersonId
OPTION(MAXRECURSION 32767);
Solution 2:
DECLARE #Base TABLE --or a temporary table: CREATE TABLE #Base (...)
(
PersonID INT NOT NULL
,StartDate DATETIME NOT NULL
,EndDate DATETIME NOT NULL
,RowNumber INT NOT NULL
,PRIMARY KEY(PersonID, RowNumber)
);
INSERT #Base (PersonID, StartDate, EndDate, RowNumber)
SELECT e.PersonId
,e.StartDate
,e.EndDate
,ROW_NUMBER() OVER(PARTITION BY e.PersonID ORDER BY e.StartDate, e.EndDate) RowNumber
FROM EventTable e;
WITH RecursiveCTE
AS
(
SELECT b.PersonId
,b.RowNumber
,b.StartDate
,b.EndDate
,b.EndDate AS MaxEndDate
,1 AS PseudoDenseRank
FROM #Base b
WHERE b.RowNumber = 1
UNION ALL
SELECT crt.PersonId
,crt.RowNumber
,crt.StartDate
,crt.EndDate
,CASE WHEN crt.EndDate > prev.MaxEndDate THEN crt.EndDate ELSE prev.MaxEndDate END
,CASE WHEN crt.StartDate <= prev.MaxEndDate THEN prev.PseudoDenseRank ELSE prev.PseudoDenseRank + 1 END
FROM RecursiveCTE prev
INNER JOIN #Base crt ON prev.PersonId = crt.PersonId
AND prev.RowNumber + 1 = crt.RowNumber
), SumDaysPerPersonAndInterval
AS
(
SELECT src.PersonId
,src.PseudoDenseRank --Interval ID
,DATEDIFF(DAY, MIN(src.StartDate), MAX(src.EndDate)) Days
FROM RecursiveCTE src
GROUP BY src.PersonId, src.PseudoDenseRank
)
SELECT x.PersonId, SUM( x.Days ) DaysPerPerson
FROM SumDaysPerPersonAndInterval x
GROUP BY x.PersonId
OPTION(MAXRECURSION 32767);