Find conflicted date intervals using SQL

Question

Suppose I have following table in Sql Server 2008:

ItemId StartDate   EndDate
1      NULL        2011-01-15
2      2011-01-16  2011-01-25
3      2011-01-26           


        

Answer 1

I've always taken a slightly different approach to the design if I have data that is never to have overlapping intervals... namely don't store intervals, but only start times. Then, have a view that helps with displaying the intervals.

CREATE TABLE intervalStarts
(
  ItemId      int,
  IntervalId  int,
  StartDate   datetime
)

CREATE VIEW intervals
AS
with cte as (
  select ItemId, IntervalId, StartDate,
     row_number() over(partition by IntervalId order by isnull(StartDate,'1753-01-01')) row
  from intervalStarts
)
select c1.ItemId, c1.IntervalId, c1.StartDate,
  dateadd(dd,-1,c2.StartDate) as 'EndDate'
from cte c1
  left join cte c2 on c1.IntervalId=c2.IntervalId
                    and c1.row=c2.row-1

So, sample data might look like:

INSERT INTO intervalStarts
select 1, 1, null union
select 2, 1, '2011-01-16' union
select 3, 1, '2011-01-26' union
select 4, 2, null union
select 5, 2, '2011-01-26' union
select 6, 2, '2011-01-14'

and a simple SELECT * FROM intervals yields:

ItemId | IntervalId | StartDate  | EndDate
1      | 1          | null       | 2011-01-15
2      | 1          | 2011-01-16 | 2011-01-25
3      | 1          | 2011-01-26 | null
4      | 2          | null       | 2011-01-13
6      | 2          | 2011-01-14 | 2011-01-25
5      | 2          | 2011-01-26 | null