问题
I have a large data set which for the purpose of this question has 3 fields:
- Group Identifier
- From Date
- To Date
On any given row the From Date will always be less than the To Date but within each group the time periods (which are in no particular order) represented by the date pairs could overlap, be contained one within another, or even be identical.
What I'd like to end up with is a query that condenses the results for each group down to just the continuous periods. For example a group that looks like this:
| Group ID | From Date | To Date |
--------------------------------------
| A | 01/01/2012 | 12/31/2012 |
| A | 12/01/2013 | 11/30/2014 |
| A | 01/01/2015 | 12/31/2015 |
| A | 01/01/2015 | 12/31/2015 |
| A | 02/01/2015 | 03/31/2015 |
| A | 01/01/2013 | 12/31/2013 |
Would result in this:
| Group ID | From Date | To Date |
--------------------------------------
| A | 01/01/2012 | 11/30/2014 |
| A | 01/01/2015 | 12/31/2015 |
I've read a number of articles on date packing but I can't quite figure out how to apply that to my data set.
How can construct a query that would give me those results?
回答1:
The solution from book "Microsoft® SQL Server ® 2012 High-Performance T-SQL Using Window Functions"
;with C1 as(
select GroupID, FromDate as ts, +1 as type, 1 as sub
from dbo.table_name
union all
select GroupID, dateadd(day, +1, ToDate) as ts, -1 as type, 0 as sub
from dbo.table_name),
C2 as(
select C1.*
, sum(type) over(partition by GroupID order by ts, type desc
rows between unbounded preceding and current row) - sub as cnt
from C1),
C3 as(
select GroupID, ts, floor((row_number() over(partition by GroupID order by ts) - 1) / 2 + 1) as grpnum
from C2
where cnt = 0)
select GroupID, min(ts) as FromDate, dateadd(day, -1, max(ts)) as ToDate
from C3
group by GroupID, grpnum;
Create table:
if object_id('table_name') is not null
drop table table_name
create table table_name(GroupID varchar(100), FromDate datetime,ToDate datetime)
insert into table_name
select 'A', '01/01/2012', '12/31/2012' union all
select 'A', '12/01/2013', '11/30/2014' union all
select 'A', '01/01/2015', '12/31/2015' union all
select 'A', '01/01/2015', '12/31/2015' union all
select 'A', '02/01/2015', '03/31/2015' union all
select 'A', '01/01/2013', '12/31/2013'
回答2:
I'd use a Calendar table. This table simply has a list of dates for several decades.
CREATE TABLE [dbo].[Calendar](
[dt] [date] NOT NULL,
CONSTRAINT [PK_Calendar] PRIMARY KEY CLUSTERED
(
[dt] ASC
))
There are many ways to populate such table.
For example, 100K rows (~270 years) from 1900-01-01:
INSERT INTO dbo.Calendar (dt)
SELECT TOP (100000)
DATEADD(day, ROW_NUMBER() OVER (ORDER BY s1.[object_id])-1, '19000101') AS dt
FROM sys.all_objects AS s1 CROSS JOIN sys.all_objects AS s2
OPTION (MAXDOP 1);
Once you have a Calendar table, here is how to use it.
Each original row is joined with the Calendar table to return as many rows as there are dates between From and To.
Then possible duplicates are removed.
Then classic gaps-and-islands by numbering the rows in two sequences.
Then grouping found islands together to get the new From and To.
Sample data
I added a second group.
DECLARE @T TABLE (GroupID int, FromDate date, ToDate date);
INSERT INTO @T (GroupID, FromDate, ToDate) VALUES
(1, '2012-01-01', '2012-12-31'),
(1, '2013-12-01', '2014-11-30'),
(1, '2015-01-01', '2015-12-31'),
(1, '2015-01-01', '2015-12-31'),
(1, '2015-02-01', '2015-03-31'),
(1, '2013-01-01', '2013-12-31'),
(2, '2012-01-01', '2012-12-31'),
(2, '2013-01-01', '2013-12-31');
Query
WITH
CTE_AllDates
AS
(
SELECT DISTINCT
T.GroupID
,CA.dt
FROM
@T AS T
CROSS APPLY
(
SELECT dbo.Calendar.dt
FROM dbo.Calendar
WHERE
dbo.Calendar.dt >= T.FromDate
AND dbo.Calendar.dt <= T.ToDate
) AS CA
)
,CTE_Sequences
AS
(
SELECT
GroupID
,dt
,ROW_NUMBER() OVER(PARTITION BY GroupID ORDER BY dt) AS Seq1
,DATEDIFF(day, '2001-01-01', dt) AS Seq2
,DATEDIFF(day, '2001-01-01', dt) -
ROW_NUMBER() OVER(PARTITION BY GroupID ORDER BY dt) AS IslandNumber
FROM CTE_AllDates
)
SELECT
GroupID
,MIN(dt) AS NewFromDate
,MAX(dt) AS NewToDate
FROM CTE_Sequences
GROUP BY GroupID, IslandNumber
ORDER BY GroupID, NewFromDate;
Result
+---------+-------------+------------+
| GroupID | NewFromDate | NewToDate |
+---------+-------------+------------+
| 1 | 2012-01-01 | 2014-11-30 |
| 1 | 2015-01-01 | 2015-12-31 |
| 2 | 2012-01-01 | 2013-12-31 |
+---------+-------------+------------+
回答3:
; with
cte as
(
select *, rn = row_number() over (partition by [Group ID] order by [From Date])
from tbl
),
rcte as
(
select rn, [Group ID], [From Date], [To Date], GrpNo = 1, GrpFrom = [From Date], GrpTo = [To Date]
from cte
where rn = 1
union all
select c.rn, c.[Group ID], c.[From Date], c.[To Date],
GrpNo = case when c.[From Date] between r.GrpFrom and dateadd(day, 1, r.GrpTo)
or c.[To Date] between r.GrpFrom and r.GrpTo
then r.GrpNo
else r.GrpNo + 1
end,
GrpFrom= case when c.[From Date] between r.GrpFrom and dateadd(day, 1, r.GrpTo)
or c.[To Date] between r.GrpFrom and r.GrpTo
then case when c.[From Date] > r.GrpFrom then c.[From Date] else r.GrpFrom end
else c.[From Date]
end,
GrpTo = case when c.[From Date] between r.GrpFrom and dateadd(day, 1, r.GrpTo)
or c.[To Date] between r.GrpFrom and dateadd(day, 1, r.GrpTo)
then case when c.[To Date] > r.GrpTo then c.[To Date] else r.GrpTo end
else c.[To Date]
end
from rcte r
inner join cte c on r.[Group ID] = c.[Group ID]
and r.rn = c.rn - 1
)
select [Group ID], min(GrpFrom), max(GrpTo)
from rcte
group by [Group ID], GrpNo
回答4:
A Geometric Approach
Here and elsewhere I've noticed that date packing questions
don't provide a geometric approach to this problem. After all,
any range, date-ranges included, can be interpreted as a line.
So why not convert them to a sql geometry type and utilize
geometry::UnionAggregate to merge the ranges. So I gave a stab
at it with your post.
Code Description
In 'numbers':
- I build a table representing a sequence
- Swap it out with your favorite way to make a numbers table.
- For a union operation, you won't ever need more rows than in your original table, so I just use it as the base to build it.
In 'mergeLines':
- I convert the dates to floats and use those floats to create geometrical points.
- In this problem, we're working in 'integer space,' meaning there are no time considerations, and so an begin date in one range that is one day apart from an end date in another should be merged with that other. In order to make that merge happen, we need to convert to 'real space.', so we add 1 to the tail of all ranges (we undo this later).
- I then connect these points via STUnion and STEnvelope.
- Finally, I merge all these lines via UnionAggregate. The resulting 'lines' geometry object might contain multiple lines, but if they overlap, they turn into one line.
In the outer query:
- I use the numbers CTE to extract the individual lines inside 'lines'.
- I envelope the lines which here ensures that the lines are stored only as its two endpoints.
- I read the endpoint x values and convert them back to their time representations, ensuring to put them back into 'integer space'.
The Code
with
numbers as (
select row_number() over (order by (select null)) i
from @spans -- Where I put your data
),
mergeLines as (
select groupId,
lines = geometry::UnionAggregate(line)
from @spans
cross apply (select
startP = geometry::Point(convert(float,fromDate), 0, 0),
stopP = geometry::Point(convert(float,toDate) + 1, 0, 0)
) pointify
cross apply (select line = startP.STUnion(stopP).STEnvelope()) lineify
group by groupId
)
select groupId, fromDate, toDate
from mergeLines ml
join numbers n on n.i between 1 and ml.lines.STNumGeometries()
cross apply (select line = ml.lines.STGeometryN(i).STEnvelope()) l
cross apply (select
fromDate = convert(datetime, l.line.STPointN(1).STX),
toDate = convert(datetime, l.line.STPointN(3).STX) - 1
) unprepare
order by groupId, fromDate;
来源：https://stackoverflow.com/questions/35498285/condense-time-periods-with-sql