消除和減少重疊的日期範圍

Question

我有一組日期範圍同時包含部分和完全重疊的日期，就像這樣：

UserID StartDate EndDate 
====== ========== ========== 
1  2011-01-01 2011-01-02 <- A 
1  2011-01-01 2011-01-10 <- A 
1  2011-01-08 2011-02-15 <- A 
1  2011-02-20 2011-03-10 <- B 
2  2011-01-01 2011-01-20 <- C 
2  2011-01-15 2011-01-25 <- C 

使用T-SQL，我想創建一個新的數據集每個用戶，以消除重複數據，擴展範圍和消除在必要的冗餘數據，從而導致這樣的事情：如果需要

UserID StartDate EndDate 
====== ========== ========== 
1  2011-01-01 2011-02-15 ('A', three rows combined, extending the range) 
1  2011-02-20 2011-03-10 ('B', no change, no overlaps here) 
2  2011-01-01 2011-01-25 ('C', two rows combined) 

光標是好的，但如果我可以毫不他們做到這一點就更好了。

Answer 1

對於SQL Server 2005+

-- sample table with data 
declare @t table(UserID int, StartDate datetime, EndDate datetime) 
insert @t select 
1, '20110101', '20110102' union all select 
1, '20110101', '20110110' union all select 
1, '20110108', '20110215' union all select 
1, '20110220', '20110310' union all select 
2, '20110101', '20110120' union all select 
2, '20110115', '20110125' 

-- your query starts below 

select UserID, Min(NewStartDate) StartDate, MAX(enddate) EndDate 
from 
(
    select *, 
     NewStartDate = t.startdate+v.number, 
     NewStartDateGroup = 
      dateadd(d, 
        1- DENSE_RANK() over (partition by UserID order by t.startdate+v.number), 
        t.startdate+v.number) 
    from @t t 
    inner join master..spt_values v 
     on v.type='P' and v.number <= DATEDIFF(d, startdate, EndDate) 
) X 
group by UserID, NewStartDateGroup 
order by UserID, StartDate 

注：

1. 替換@t您的表名