可用日期范围（按年份）

Question

I have a table that holds date

ID      Dates
1       2014-01-20
2       2014-01-21
...
100     2014-05-20 
101     2014-06-01  --Missing a few dates
102     2014-06-02
...
201     2014-10-31
202     2014-12-05  --Missing a few dates
...
349     2015-04-29
350     2015-04-30

I want to find the available date range by year between a from and to date, for example

@StartDate: 2014/04/06
@EndDate: 2015/04/05

The expected result is

Year    StartRange      EndRange
2014    2014-04-06      2014-05-20
2014    2014-06-01      2014-10-31
2014    2014-12-05      2014-12-31
2015    2015-01-01      2015-04-05

I am trying to find the available date ranges from the Dates column. Lets take the first row in the expected result 2014-04-06 to 2014-05-20 which says I have continuous dates from the 6th April to 20th May then there is a break (I do not have dates from 2014-05-21 to 2014-05-30)

The dates 2014-04-06 (in the first row) and 2015-04-05 (in the last row) are included in the expected result as it is the start and end date (parameter to the query) and I have those dates in the [Dates] column of my table

Thanks

Answer 1

This is an "Islands and Gaps" type of problem. Here is one way to do it:

;
WITH
  cteDays As (SELECT *, DATEDIFF(dd,0,Dates) As DayNo From YourTable)
, cteDifs As 
(
    SELECT *, 
        DayNo-(ROW_NUMBER() OVER(ORDER BY Dates, ID)) As Dif
    FROM    cteDays
)
SELECT
    Year(Dates) As [Year],
    MIN(Dates)  As StartRange,
    MAX(Dates)  As EndRange
FROM    cteDifs
GROUP BY Year(Dates), Dif
ORDER BY [Year], StartRange