SELECT statement that shows continuous data with condition - sql

Question

I consider myself good at SQL but failed at this problem.
I need a SELECT statement that shows all rows above 100 if there are
3 rows or more with 100 next to it.
Given Table "Trend":
| id | volume |
+----+---------+
| 0 | 200 |
| 1 | 90 |
| 2 | 101 |
| 3 | 120 |
| 4 | 200 |
| 5 | 10 |
| 6 | 400 |
I need a SELECT statement to produce:
| 2 | 101 |
| 3 | 120 |
| 4 | 200 |

Answer 1

I suspect that you are after the following logic:
select *
from (
select t.*,
sum(case when volume > 100 then 1 else 0 end) over(order by id rows between 2 preceding and 2 following) cnt
from mytable t
) t
where volume > 100 and cnt >= 3
This counts how many values are above 100 in the range made of the two preceding rows, the current row and the next two rows. Then we filter on rows whose window count is 3 or more.
This uses a syntax that most database support (provided that window functions are available). Neater expressions may be available depending on the actual database you are using.
In MySQL:
sum(volume > 100) over(order by id rows between 2 preceding and 2 following) cnt
In Postgres:
count(*) filter(where volume > 100) over(order by id rows between 2 preceding and 2 following) cnt
Or:
sum((volume > 100)::int) over(order by id rows between 2 preceding and 2 following) cnt

Answer 2

This is tricky because you want the original rows . . . I am going to suggest lag() and lead():
select id, volume
from (select t.*,
lag(volume, 2) over (order by id) as prev_volume_2,
lag(volume) over (order by id) as prev_volume,
lead(volume, 2) over (order by id) as next_volume_2,
lead(volume) over (order by id) as next_volume
from t
) t
where volume > 100 and
( (prev_volume_2 > 100 and prev_volume > 100) or
(prev_volume > 100 and next_volume > 100) or
(next_volume_2 > 100 and next_volume > 100)
);
Another method is to treat this as a gaps-and-islands problem. This makes the solution more generalizable. You can assign a group by counting the number of rows less than or equal to 100 up to each row. Then count the number that are greater than 100 to see if those groups qualify to be in the final results:
select id, volume
from (select t.*,
sum(case when volume > 100 then 1 else 0 end) over (partition by grp) as cnt
from (select t.*,
sum(case when volume <= 100 then 1 else 0 end) over (order by id) as grp
from t
) t
) t
where volume > 100 and cnt >= 3;
Here is a db<>fiddle with these two approaches.

Answer 3

Key point here is "3 rows or more". MATCH_RECOGNIZE could be used:
SELECT *
FROM trend
MATCH_RECOGNIZE (
ORDER BY id -- ordering of a streak
MEASURES FINAL COUNT(*) AS l -- count "per" match
ALL ROWS PER MATCH -- get all rows
PATTERN(a{3,}) -- 3 or more
DEFINE a AS volume >= 100 -- condtion of streak
)
ORDER BY l DESC FETCH FIRST 1 ROWS WITH TIES;
-- choose the group that has the longest streak
The strength of this approach is a PATTERN part which could be modifed to handle different scenarios like a{3,5} - between 3 and 5 occurences, a{4} exactly 4 occurences and so on. More conditions could be defined which allows to build complex pattern detection.
db<>fiddle demo

Answer 4

Get the min value of volume for all consecutive 3 rows of the table.
Then join to the table and keep only the ones belonging to a group that has min > 100:
select distinct t.*
from Trend t
inner join (
select t.*,
min(t.volume) over (order by t.id rows between current row and 2 following) min_volume,
lead(t.id, 1) over (order by t.id) next1,
lead(t.id, 2) over (order by t.id) next2
from Trend t
) m on t.id in (m.id, m.next1, m.next2)
where m.min_volume > 100 and m.next1 is not null and m.next2 is not null
See the demo for SQL Server, MySql, Postgresql, Oracle, SQLite.
Results:
> id | volume
> -: | -----:
> 2 | 101
> 3 | 120
> 4 | 200

Answer 5

a simplistic approach:
--CREATE TABLE Trend (id integer, volume integer);
--insert into Trend VALUES
-- (0,200),
-- (1,90),
-- (2,101),
-- (3,120),
-- (4,200),
-- (5,10),
-- (6,400);
SELECT
t1.id, t1.volume
--,t2.id, t2.volume
--,t3.id, t3.volume
FROM Trend t1
INNER JOIN Trend t2 ON t2.id>t1.id and t2.volume>100 and not exists (select * from Trend t5 where t5.id between t1.id+1 and t2.id-1)
INNER JOIN Trend t3 ON t3.id>t2.id and t3.volume>100 and not exists (select * from Trend where id between t2.id+1 and t3.id-1)
WHERE t1.volume>100
union all
SELECT
--t1.id, t1.volume
t2.id, t2.volume
--,t3.id, t3.volume
FROM Trend t1
INNER JOIN Trend t2 ON t2.id>t1.id and t2.volume>100 and not exists (select * from Trend t5 where t5.id between t1.id+1 and t2.id-1)
INNER JOIN Trend t3 ON t3.id>t2.id and t3.volume>100 and not exists (select * from Trend where id between t2.id+1 and t3.id-1)
WHERE t1.volume>100
union all
SELECT
--t1.id, t1.volume
--t2.id, t2.volume
t3.id, t3.volume
FROM Trend t1
INNER JOIN Trend t2 ON t2.id>t1.id and t2.volume>100 and not exists (select * from Trend t5 where t5.id between t1.id+1 and t2.id-1)
INNER JOIN Trend t3 ON t3.id>t2.id and t3.volume>100 and not exists (select * from Trend where id between t2.id+1 and t3.id-1)
WHERE t1.volume>100