hard tsql problem - how many row values are in a sequential order - sql

Question

lets say I have a table with
date,personid
1/1/2001 1
1/2/2001 3
1/3/2001 2
1/4/2001 2
1/5/2001 5
1/6/2001 5
1/7/2001 6
and I'm going to either update 1/2/2001 or 1/5/2001 with personid 2 but before I can update I have to make sure it passes a rule that says you can't have a person three days in a row.
how can i solve this in a mssql stored procedure?
update: It also need to solve this layout as well where I'd update 1/5/2001
date,personid
1/1/2001 1
1/2/2001 3
1/3/2001 2
1/4/2001 2
1/5/2001 1
1/6/2001 2
1/7/2001 2
1/8/2001 5
1/9/2001 5
1/10/2001 6

Answer 1

I've assumed that date is unique let me know if that is not the case!
DECLARE #basedata TABLE ([date] UNIQUE DATE,personid INT)
INSERT INTO #basedata
SELECT GETDATE()+1, 2 union all
SELECT GETDATE()+2, 3 union all
SELECT GETDATE()+3, 2 union all
SELECT GETDATE()+4, 2 union all
SELECT GETDATE()+5, 5 union all
SELECT GETDATE()+6, 5 union all
SELECT GETDATE()+7, 6
DECLARE #date date = GETDATE()+5
DECLARE #personid int = 2
;WITH T AS
(
SELECT TOP 2 [date],personid
FROM #basedata
WHERE [date] < #date
ORDER BY [date] DESC
UNION ALL
SELECT #date, #personid
UNION ALL
SELECT TOP 2 [date],personid
FROM #basedata
WHERE [date] > #date
ORDER BY [date]
),T2 AS
(
SELECT *,
ROW_NUMBER() OVER (ORDER BY [date]) -
ROW_NUMBER() OVER (PARTITION BY personid ORDER BY [date]) AS Grp
FROM T
)
SELECT COUNT(*) /*Will return a result if that date/personid
would cause a sequence of 3*/
FROM T2
GROUP BY personid,Grp
HAVING COUNT(*) >=3

Answer 2

There is a third case not listed, it is the between date case. I included it in the solution below.
The output is
PersonId TrackDate UnallowedBefore UnallowedAfter
----------- ---------- --------------- --------------
2 01/04/2001 01/02/2001 01/05/2001
5 01/06/2001 01/04/2001 01/07/2001
6 01/08/2001 01/08/2001 01/08/2001
USE tempdb
GO
IF OBJECT_ID('PersonDates') IS NOT NULL DROP TABLE PersonDates
CREATE TABLE PersonDates
(
PersonId int NOT NULL,
TrackDate datetime NOT NULL
)
INSERT INTO PersonDates
(
TrackDate,
PersonId
)
SELECT '1/1/2001', 1
UNION ALL
SELECT '1/2/2001', 3
UNION ALL
SELECT '1/3/2001', 2
UNION ALL
SELECT '1/4/2001', 2
UNION ALL
SELECT '1/5/2001', 5
UNION ALL
SELECT '1/6/2001', 5
UNION ALL
SELECT '1/7/2001', 6
UNION ALL
SELECT '1/8/2001', 2
UNION ALL
SELECT '1/9/2001', 6
SELECT
P.PersonId,
TrackDate = CONVERT(varchar(10), DATEADD(day, 1, P.TrackDate), 101),
T.UnallowedBefore,
T.UnallowedAfter
FROM
PersonDates P
CROSS APPLY
(
SELECT TOP 1
UnallowedAfter = CASE
WHEN DATEDIFF(day, P.TrackDate, TrackDate) = 1
THEN CONVERT(varchar(10), DATEADD(day, 1, TrackDate), 101)
ELSE CONVERT(varchar(10), DATEADD(day, -1, TrackDate), 101)
END,
UnallowedBefore = CASE
WHEN DATEDIFF(day, P.TrackDate, TrackDate) = 1
THEN CONVERT(varchar(10), DATEADD(day, -2, TrackDate), 101)
ELSE CONVERT(varchar(10), DATEADD(day, -1, TrackDate), 101)
END
FROM
PersonDates
WHERE
PersonId = P.PersonId
AND
DATEDIFF(day, P.TrackDate, TrackDate) IN (1,2)
) T

Answer 3

SET #TargetDate = '1/2/2001'
SELECT #ForwardCount = COUNT(*) FROM table WHERE ([date] BETWEEN #TargetDate AND DATEADD(dd, 2, #TargetDate)) WHERE PersonID = #PersonID
SELECT #BackwardCount = COUNT(*) FROM table WHERE ([date] BETWEEN #TargetDate AND DATEADD(dd, -2, #TargetDate)) WHERE PersonID = #PersonID
SELECT #BracketCount = COUNT(*) FROM table WHERE ([date] BETWEEN DATEADD(dd, -1, #TargetDate) AND DATEADD(dd, 1, #TargetDate)) WHERE PersonID = #PersonID
IF (#ForwardCount < 2) AND (#BackwardCount < 2) AND (#BracketCount < 2)
BEGIN
-- Do your update here
END

Answer 4

Here's my parametrised solution:
WITH nearby AS (
SELECT
date,
personid = CASE date WHEN #date THEN #personid ELSE personid END
FROM atable
WHERE date BETWEEN DATEADD(day, -#MaxInARow, #date)
AND DATEADD(day, #MaxInARow, #date)
),
nearbyGroups AS (
SELECT
*,
Grp = DATEDIFF(day, 0, date) -
ROW_NUMBER() OVER (PARTITION BY personid ORDER BY date)
FROM nearby
)
UPDATE atable
SET personid = #personid
WHERE date = #date
AND NOT EXISTS (
SELECT Grp
FROM nearbyGroups
GROUP BY Grp
HAVING COUNT(*) > #MaxInARow
)
#date represents the date for which the personid column should be updated. #personid is the new value to be stored. #MaxInARow is the maximum number of days in a row for which the same personid is allowed to be stored.