How to merge time intervals in SQL Server

Question

Suppose I have the following an event table with personId, startDate and endDate.

I want to know how much time the person X sp

Answer 1

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 2

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);

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

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 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