Flatten/merge overlapping time intervals - sql-server

Question

I have a 'Service' table with millions of rows. Each row corresponds to a service provided by a staff in a given date and time interval (Each row has a unique ID). There are cases where a staff might provide services in overlapping time frames. I need to write a query that merges overlapping time intervals and returns the data in the format shown below.
I tried grouping by StaffID and Date fields and getting the Min of BeginTime and Max of EndTime but that does not account for the non-overlapping time frames. How can I accomplish this? Again, the table contains several million records so a recursive CTE approach might have performance issues. Thanks in advance.
Service Table
ID StaffID Date BeginTime EndTime
1 101 2014-01-01 08:00 09:00
2 101 2014-01-01 08:30 09:30
3 101 2014-01-01 18:00 20:30
4 101 2014-01-01 19:00 21:00
Output
StaffID Date BeginTime EndTime
101 2014-01-01 08:00 09:30
101 2014-01-01 18:00 21:00
Here is another sample data set with a query proposed by a contributor.
http://sqlfiddle.com/#!6/bfbdc/3
The first two rows in the results set should be merged into one row (06:00-08:45) but it generates two rows (06:00-08:30 & 06:00-08:45)

Answer 1

I only came up with a CTE query as the problem is there may be a chain of overlapping times, e.g. record 1 overlaps with record 2, record 2 with record 3 and so on. This is hard to resolve without CTE or some other kind of loops, etc. Please give it a go anyway.
The first part of the CTE query gets the services that start a new group and are do not have the same starting time as some other service (I need to have just one record that starts a group). The second part gets those that start a group but there's more then one with the same start time - again, I need just one of them. The last part recursively builds up on the starting group, taking all overlapping services.
Here is SQLFiddle with more records added to demonstrate different kinds of overlapping and duplicate times.
I couldn't use ServiceID as it would have to be ordered in the same way as BeginTime.
;with flat as
(
select StaffID, ServiceDate, BeginTime, EndTime, BeginTime as groupid
from services S1
where not exists (select * from services S2
where S1.StaffID = S2.StaffID
and S1.ServiceDate = S2.ServiceDate
and S2.BeginTime <= S1.BeginTime and S2.EndTime <> S1.EndTime
and S2.EndTime > S1.BeginTime)
union all
select StaffID, ServiceDate, BeginTime, EndTime, BeginTime as groupid
from services S1
where exists (select * from services S2
where S1.StaffID = S2.StaffID
and S1.ServiceDate = S2.ServiceDate
and S2.BeginTime = S1.BeginTime and S2.EndTime > S1.EndTime)
and not exists (select * from services S2
where S1.StaffID = S2.StaffID
and S1.ServiceDate = S2.ServiceDate
and S2.BeginTime < S1.BeginTime
and S2.EndTime > S1.BeginTime)
union all
select S.StaffID, S.ServiceDate, S.BeginTime, S.EndTime, flat.groupid
from flat
inner join services S
on flat.StaffID = S.StaffID
and flat.ServiceDate = S.ServiceDate
and flat.EndTime > S.BeginTime
and flat.BeginTime < S.BeginTime and flat.EndTime < S.EndTime
)
select StaffID, ServiceDate, MIN(BeginTime) as begintime, MAX(EndTime) as endtime
from flat
group by StaffID, ServiceDate, groupid
order by StaffID, ServiceDate, begintime, endtime

Answer 2

Elsewhere I've answered a similar Date Packing question with
a geometric strategy. Namely, I interperet the date ranges
as a line, and utilize geometry::UnionAggregate to merge
the ranges.
Your question has two peculiarities though. First, it calls
for sql-server-2008. geometry::UnionAggregate is not then
avialable. However, download the microsoft library at
https://github.com/microsoft/SQLServerSpatialTools and load
it in as a clr assembly to your instance and you have it
available as dbo.GeometryUnionAggregate.
But the real peculiarity that has my interest is the concern
that you have several million rows to work with. So I thought
I'd repeat the strategy here but with an added technique to
improve it's performance. This technique will work well if
you have a lot of your StaffID/date subsets that are the same.
First, let's build a numbers table. Swap this out with your favorite
way to do it.
select i = row_number() over (order by (select null))
into #numbers
from #services; -- where i put your data
Then convert the dates to floats and use those floats to create
geometrical points.
These points can then be turned into lines via STUnion and STEnvelope.
With your ranges now represented as geometric lines, merge them via
UnionAggregate. The resulting geometry object 'lines' might contain
multiple lines. But any overlapping lines turn into one line.
select s.StaffID,
s.Date,
linesWKT = geometry::UnionAggregate(line).ToString()
-- If you have SQLSpatialTools installed then:
-- linesWKT = dbo.GeometryUnionAggregate(line).ToString()
into #aggregateRangesToGeo
from #services s
cross apply (select
beginTimeF = convert(float, convert(datetime,beginTime)),
endTimeF = convert(float, convert(datetime,endTime))
) prepare
cross apply (select
beginPt = geometry::Point(beginTimeF, 0, 0),
endPt = geometry::Point(endTimeF, 0, 0)
) pointify
cross apply (select
line = beginPt.STUnion(endPt).STEnvelope()
) lineify
group by s.StaffID,
s.Date;
You have one 'lines' object for each staffId/date combo. But depending
on your dataset, there may be many 'lines' objects that are the same
between these combos. This may very well be true if staff are expected
to follow a routine and data is recorded to the nearest whatever.
So get a distinct lising of 'lines' objects. This should improve
performance.
From this, extract the individual lines inside 'lines'. Envelope the lines,
which ensures that the lines are stored only as their endpoints. Read the
endpoint x values and convert them back to their time representations.
Keep the WKT representation to join it back to the combos later on.
select lns.linesWKT,
beginTime = convert(time, convert(datetime, ap.beginTime)),
endTime = convert(time, convert(datetime, ap.endTime))
into #parsedLines
from (select distinct linesWKT from #aggregateRangesToGeo) lns
cross apply (select
lines = geometry::STGeomFromText(linesWKT, 0)
) geo
join #numbers n on n.i between 1 and geo.lines.STNumGeometries()
cross apply (select
line = geo.lines.STGeometryN(n.i).STEnvelope()
) ln
cross apply (select
beginTime = ln.line.STPointN(1).STX,
endTime = ln.line.STPointN(3).STX
) ap;
Now just join your parsed data back to the StaffId/Date combos.
select ar.StaffID,
ar.Date,
pl.beginTime,
pl.endTime
from #aggregateRangesToGeo ar
join #parsedLines pl on ar.linesWKT = pl.linesWKT
order by ar.StaffID,
ar.Date,
pl.beginTime;