Get consecutive days with condition - sql

Question

There is a table with three columns:
CREATE TABLE #t1 ( Id INT
,VisitDate DATE
,Counter INT)
AND test data:
INSERT INTO #t1 VALUES (1,'2019-01-01', 50)
INSERT INTO #t1 VALUES (2,'2019-01-02', 15)
INSERT INTO #t1 VALUES (3,'2019-01-03', 7)
INSERT INTO #t1 VALUES (4,'2019-01-04', 7)
INSERT INTO #t1 VALUES (5,'2019-01-05', 18)
INSERT INTO #t1 VALUES (6,'2019-01-06', 19)
INSERT INTO #t1 VALUES (7,'2019-01-07', 11)
INSERT INTO #t1 VALUES (8,'2019-01-08', 1)
INSERT INTO #t1 VALUES (9,'2019-01-09', 19)
Need to find three and more consecutive days where Counter more or equal ten:
Id VisitDate Counter
5 2019-01-05 18
6 2019-01-06 19
7 2019-01-07 11
My SELECT statement is
;WITH cte AS
(
SELECT *
,IIF(Counter > 10, 1,0) AS MoreThanTen
FROM #t1
), lag_lead_cte AS
(
SELECT *
,LAG(MoreThanTen) OVER (ORDER BY VisitDate) AS LagShift
,(LAG(MoreThanTen) OVER (ORDER BY VisitDate) + MoreThanTen ) AS LagMoreThanTen
,LEAD(MoreThanTen) OVER (ORDER BY VisitDate) AS LeadShift
,(LEAD(MoreThanTen) OVER (ORDER BY VisitDate) + MoreThanTen ) AS LeadMoreThanTen
FROM cte
)
SELECT *
FROM lag_lead_cte
WHERE LagMoreThanTen = 2 OR LeadMoreThanTen = 2
But the result is not fully consistent
Id VisitDate Counter
1 2019-01-01 50
2 2019-01-02 15
5 2019-01-05 18
6 2019-01-06 19
7 2019-01-07 11

Answer 1

It looks like a gaps-and-islands problem.
Here is one way to do it.
I'm assuming SQL Server based on the T-SQL tag.
Run this query CTE-by-CTE and examine intermediate results to understand how it works.
Query
WITH
CTE_rn
AS
(
SELECT *
,CASE WHEN Counter>10 THEN 1 ELSE 0 END AS MoreThanTen
,ROW_NUMBER() OVER (ORDER BY VisitDate) AS rn1
,ROW_NUMBER() OVER (PARTITION BY CASE WHEN Counter>10 THEN 1 ELSE 0 END ORDER BY VisitDate) AS rn2
FROM #t1
)
,CTE_Groups
AS
(
SELECT
*
,rn1-rn2 AS Diff
,COUNT(*) OVER (PARTITION BY MoreThanTen, rn1-rn2) AS GroupLength
FROM CTE_rn
)
SELECT
ID
,VisitDate
,Counter
FROM CTE_Groups
WHERE
GroupLength >= 3
AND Counter > 10
ORDER BY VisitDate
;
Result
+----+------------+---------+
| ID | VisitDate | Counter |
+----+------------+---------+
| 5 | 2019-01-05 | 18 |
| 6 | 2019-01-06 | 19 |
| 7 | 2019-01-07 | 11 |
+----+------------+---------+

Answer 2

Try this:
select Id, VisitDate, Counter from (
select Id, VisitDate, Counter, count(*) over (partition by grp) cnt from (
select *,
-- here I used difference between row number and day to group consecutive days
row_number() over (order by visitDate) - day(visitDate) grp
from #t1
where [Counter] > 10
) a
) a where cnt >= 3 --where group count is greater or equal to three
Based on the comment that days does not need to be consecutive, just rows have to be consecutive, here is updated query, which uses similair technique:
select id, visitdate, counter from (
select id, visitdate, counter, count(*) over (partition by grp) cnt from (
select *, rn - row_number() over (order by visitDate) grp from (
select *,
case when (Counter > 10) or (lag(Counter) over (order by visitDate) > 10 and Counter > 10) then
row_number() over (order by visitdate) end rn
from #t1
) a where rn is not null
) a
) a where cnt >= 3

Answer 3

I think this might be most simply handled by just looking at the sequences using lead() and lag():
select id, visitdate, counter
from (select t1.*,
lag(counter, 2) over (order by visitdate) as counter_2p,
lag(counter, 1) over (order by visitdate) as counter_1p,
lead(counter, 1) over (order by visitdate) as counter_1l,
lead(counter, 2) over (order by visitdate) as counter_2l
from t1
) t1
where counter >= 10 and
((counter_2p >= 10 and counter_1p >= 10) or
(counter_1p >= 10 and counter_1l >= 10) or
(counter_1l >= 10 and counter_2l >= 10)
);

Answer 4

Cross apply also works for this Question
with result as (
select
t.Id as Id1,t.VisitDate as VisitDate1,t.Counter as Counter1
,tt.Id as Id2,tt.VisitDate as VisitDate2,tt.Counter as Counter2
from #t1 t cross join #t1 tt where DATEDIFF(Day,t.VisitDate,tt.visitDate)=1
and t.Counter>10 and tt.Counter>10
)
select Id1 as Id,VisitDate1 as VisitDate ,Counter1 as [Counter] from result
union
select Id2 as Id,VisitDate2 as VisitDate,Counter2 as [Counter] from result