Question

Given the following set of data, I’m trying to determine how I can select the start and end dates of the combined date ranges, when they intersect with each other.

For instance, for PartNum 115678, I would want my final result set to display the date ranges 2012/01/01 - 2012/01/19 (rows 1, 2 and 4 combined since the date ranges intersect) and 2012/02/01 - 2012/03/28 (row 3 since this ones does not intersect with the range found previously).

For PartNum 213275, I would want to select the only row for that part, 2012/12/01 - 2013/01/01.

Edit:
I’m currently playing around with the following SQL statement, but it’s not giving me exactly what I need.

with DistinctRanges as (
    select distinct
        ha1.PartNum "PartNum",
        ha1.StartDt "StartDt",
        ha2.EndDt "EndDt"
    from dbo.HoldsAll ha1
    inner join dbo.HoldsAll ha2 
        on ha1.PartNum = ha2.PartNum
    where 
        ha1.StartDt <= ha2.EndDt 
        and ha2.StartDt <= ha1.EndDt
)
select 
    PartNum, 
    StartDt, 
    EndDt
from DistinctRanges

Here are the results of the query shown in the edit:

Answer 1

You’re better off having a persisted Calendar table, but if you don’t, the CTE below will create it ad-hoc. The TOP(36000) part is enough to give you 10 years worth of dates from the pivot ('20100101') on the same line.

SQL Fiddle

MS SQL Server 2008 Schema Setup:

create table data (
    partnum int,
    startdt datetime,
    enddt datetime,
    age int
);
insert data select 
12345, '20120101', '20120116', 15 union all select
12345, '20120115', '20120116', 1 union all select
12345, '20120201', '20120328', 56 union all select
12345, '20120113', '20120119', 6 union all select
88872, '20120201', '20130113', 43;

Query 1:

with Calendar(thedate) as (
    select TOP(36600) dateadd(d,row_number() over (order by 1/0),'20100101')
      from sys.columns a
cross join sys.columns b
cross join sys.columns c
), tmp as (
   select partnum, thedate,
          grouper = datediff(d, dense_rank() over (partition by partnum order by thedate), thedate)
     from Calendar c
     join data d on d.startdt <= c.thedate and c.thedate <= d.enddt
)
select partnum, min(thedate) startdt, max(thedate) enddt
  from tmp
 group by partnum, grouper
 order by partnum, startdt

Results:

| PARTNUM |                         STARTDT |                          ENDDT |
------------------------------------------------------------------------------
|   12345 |  January, 01 2012 00:00:00+0000 | January, 19 2012 00:00:00+0000 |
|   12345 | February, 01 2012 00:00:00+0000 |   March, 28 2012 00:00:00+0000 |
|   88872 | February, 01 2012 00:00:00+0000 | January, 13 2013 00:00:00+0000 |