select a chain of records using mssql - sql

Question

I have a table with records in TimeLines, I need to get rows that form a chain of 45 minutes set.
1|2016-01-01 00:00
2|2016-01-01 00:30
3|2016-01-01 00:45
4|2016-01-01 01:00
How I can find 2nd row depending from it time, cause 2nd, 3rd and 4th rows are indissoluble 15 minutes chain of timeline for 45 min set?
1st and 2nd is not okay, cause interval between timelines is 30 min.
2nd, 3rd and 4th rows are consistent chain of timeline.
2nd row plus 15 min - okay. cause existed 3rd row with that time.
3rd row plus 15 min - okay. cause existed 4th row with that time.
as result i have 45 min consistent timeline chain.
1row plus 15 min - not okay. cause 00:15 time with date not existed.

Answer 1

Try this
DECLARE #Tbl TABLE (Id INT, StartDate DATETIME)
INSERT INTO #Tbl
VALUES
(1,'2016-01-01 00:00'),
(2,'2016-01-01 00:30'),
(3,'2016-01-01 00:45'),
(4,'2016-01-01 01:00')
;WITH CTE
AS
(
SELECT
Id ,
StartDate,
ROW_NUMBER() OVER (ORDER BY Id) AS RowId
FROM
#Tbl
)
SELECT
CurRow.*,
CASE
WHEN
DATEDIFF(MINUTE, CurRow.StartDate, NextRow.StartDate ) = 15 OR
DATEDIFF(MINUTE, PrevRow.StartDate, CurRow.StartDate ) = 15
THEN '15 MIN'
ELSE 'NO' END Flag
FROM
CTE CurRow LEFT JOIN
(SELECT *, C.RowId - 1 AS TmpRowId FROM CTE C) NextRow ON CurRow.RowId = NextRow.TmpRowId LEFT JOIN
(SELECT *, C.RowId + 1 AS TmpRowId FROM CTE C) PrevRow ON CurRow.RowId = PrevRow.TmpRowId
OUTPUT:
Id StartDate RowId Flag
1 2016-01-01 00:00:00.000 1 NO
2 2016-01-01 00:30:00.000 2 15 MIN
3 2016-01-01 00:45:00.000 3 15 MIN
4 2016-01-01 01:00:00.000 4 15 MIN

Answer 2

If I understand you correctly, you can use LEAD/LAG:
WITH Src AS
(
SELECT * FROM (VALUES
(1,'2016-01-01 00:00'),
(2,'2016-01-01 00:30'),
(3,'2016-01-01 00:45'),
(4,'2016-01-01 01:00')) T(ID, [Date])
)
SELECT *, CASE WHEN LEAD([Date]) OVER (ORDER BY ID)=DATEADD(MINUTE, 15, [Date])
OR LAG([Date]) OVER (ORDER BY ID)=DATEADD(MINUTE, -15, [Date])
THEN 'Chained' END [Status]
FROM Src
It produces:
ID Date Status
-- ---- ------
1 2016-01-01 00:00 NULL
2 2016-01-01 00:30 Chained
3 2016-01-01 00:45 Chained
4 2016-01-01 01:00 Chained

Answer 3

You can do this with OUTER APPLY and tricky ROW_NUMBER():
;WITH TimeLines AS ( --This CTE is similar to your table
SELECT *
FROM (VALUES
(1, '2016-01-01 00:00'),(2, '2016-01-01 00:30'),
(3, '2016-01-01 00:45'),(4, '2016-01-01 01:00'),
(5, '2016-01-01 01:05'),(6, '2016-01-01 01:07'),
(7, '2016-01-01 01:15'),(8, '2016-01-01 01:30'),
(9, '2016-01-01 01:45'),(10, '2016-01-01 02:00')
) as t(id, datum)
)
, cte AS (
SELECT t.id,
t.datum,
CASE WHEN ISNULL(DATEDIFF(MINUTE,t1.datum,t.datum),0) != 15 THEN DATEDIFF(MINUTE,t.datum,t2.datum) ELSE 15 END as i
FROM TimeLines t --in this cte with the help of
OUTER APPLY ( --OUTER APPLY we are getting next and previous dates to compare them
SELECT TOP 1 *
FROM TimeLines
WHERE t.datum > datum
ORDER BY datum desc) t1
OUTER APPLY (
SELECT TOP 1 *
FROM TimeLines
WHERE t.datum < datum
ORDER BY datum asc) t2
)
SELECT *, --this is final select to get rows you need with chaines
(ROW_NUMBER() OVER (ORDER BY (SELECT 1))+2)/3 as seq
FROM cte
WHERE i = 15
Output:
id datum i seq
2 2016-01-01 00:30 15 1
3 2016-01-01 00:45 15 1
4 2016-01-01 01:00 15 1
7 2016-01-01 01:15 15 2
8 2016-01-01 01:30 15 2
9 2016-01-01 01:45 15 2
10 2016-01-01 02:00 15 3