Overlapping Spans - sql

Question

I am trying to write a query that reorders date ranges around particular spans. It should do something that looks like this
Row Rank Begin Date End Date
1 B 3/24/13 11/1/13
2 A 10/30/13 4/9/15
3 B 3/26/15 12/31/15
and have it become
Row Rank Begin Date End Date
1 B 3/24/13 10/29/13
2 A 10/30/13 4/9/15
3 B 4/10/15 12/31/15
To explain further, the dates in row 2 is ranked higher (A>B), so the dates in row 1 and 3 have to change around the dates in row 2 in order to avoid overlap in dates.
I am using SQL Server 2008 R2

Answer 1

You can use the following query:
;WITH CTE AS (
SELECT Row, Rank, BeginDate, EndDate,
ROW_NUMBER() OVER (ORDER BY BeginDate) AS rn
FROM mytable
), ToUpdate AS (
SELECT c1.Row, c1.Rank, c1.BeginDate, c1.EndDate,
c2.Rank AS pRank, c2.EndDate AS pEndDate,
c3.Rank AS nRank, c3.BeginDate AS nBeginDate
FROM CTE AS c1
LEFT JOIN CTE AS c2 ON c1.rn = c2.rn + 1
LEFT JOIN CTE AS c3 ON c1.rn = c3.rn - 1
WHERE c1.Rank = 'B'
)
UPDATE ToUpdate
SET BeginDate = CASE
WHEN pEndDate IS NULL
THEN BeginDate
WHEN (pEndDate >= BeginDate) AND (pRank = 'A')
THEN DATEADD(d, 1, pEndDate)
ELSE BeginDate
END,
EndDate = CASE
WHEN nBeginDate IS NULL
THEN EndDate
WHEN (nBeginDate <= EndDate) AND (nRank = 'A')
THEN DATEADD(d, -1, nBeginDate)
ELSE EndDate
END
A CTE is initially constructed to assign consecutive, ascending numbers to every record of your table. ROW_NUMBER() window function is used for this purpose.
Using this CTE as a basis we construct ToUpdate. This latter CTE contains date values of current as well as previous and next records.
This LEFT JOIN:
LEFT JOIN CTE AS c2 ON c1.rn = c2.rn + 1
is used to join together with previous record, whereas this one:
LEFT JOIN CTE AS c3 ON c1.rn = c3.rn - 1
is used to join together with next record.
Using CASE expressions we can now easily identify overlaps, and, in case there is one, perform an update.
Demo here

Answer 2

Please use the below query to update the table.
Update table_name
set End_Date = DATEADD(day, -1, select Begin_Date from Table_name where
Row_number = '2')
where row = 1;
You need to change the row numbers every time you run the query. Let me know If this works for you.
I suggest First create a View
CREATE OR REPLACE VIEW tempview AS
SELECT row, begin_date FROM table_name
WHERE row > 1;
Then Use this query to update all the row. If may not update just the first row.
Update table_name
set End_Date = DATEADD(day, -1, select Begin_Date from tempview)
Hope this works