how to get current streak in mysql - mysql

Question

I am trying to create a query for getting the current streak in MySQL based on status
ID
Dated
Status
1
2022-03-08
1
2
2022-03-09
1
3
2022-03-10
0
4
2022-03-11
1
5
2022-03-12
0
6
2022-03-13
1
7
2022-03-14
1
8
2022-03-16
1
9
2022-03-18
0
10
2022-03-19
1
11
2022-03-20
1
In the above table current streak should be 2( i.e 2022-03-20 - 2022-03-19) based on status 1. Any help or ideas would be greatly appreciated!

Answer 1

WITH cte AS (
SELECT SUM(Status) OVER (ORDER BY Dated DESC) s1,
SUM(NOT Status) OVER (ORDER BY Dated DESC) s2
FROM table
)
SELECT MAX(s1)
FROM cte
WHERE NOT s2;
SELECT DATEDIFF(MAX(CASE WHEN Status THEN Dated END),
MAX(CASE WHEN NOT Status THEN Dated END))
FROM table
and so on...

Answer 2

This is a gaps and islands problem. In your case, you want the island of status 1 records which occurs last. We can use the difference in row numbers method, assuming you are using MySQL 8+.
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (ORDER BY Dated) rn1,
ROW_NUMBER() OVER (PARTITION BY Status ORDER BY Dated) rn2
FROM yourTable
),
cte2 AS (
SELECT *, RANK() OVER (ORDER BY rn1 - rn2 DESC) rnk
FROM cte
WHERE Status = 1
)
SELECT ID, Dated, Status
FROM cte2
WHERE rnk = 1
ORDER BY Dated;
Demo

Answer 3

We can use 2 one row CTE's to find the latest date where the status was not the same as the latest one and then count the records superieur.
**Schema (MySQL v8.0)**
create table t(
ID int,
Dated date,
Status int);
insert into t values
(1,'2022-03-08',1),
(2,'2022-03-09',1),
(3,'2022-03-10',0),
(4,'2022-03-11',1),
(5,'2022-03-12',0),
(6,'2022-03-13',1),
(7,'2022-03-14',1),
(8,'2022-03-16',1),
(9,'2022-03-18',0),
(10,'2022-03-19',1),
(11,'2022-03-20',1);
---
**Query #1**
with latest AS
(SELECT
dated lastDate,
status lastStatus
from t
order by dated desc
limit 1 ),
lastDiff as
(select MAX(dated) diffDate
from t,latest
where not status = lastStatus
)
select count(*)
from t ,lastDiff
where dated > diffDate;
| count(*) |
| -------- |
| 2 |
---
[View on DB Fiddle](https://www.db-fiddle.com/)
We could also consider using datediff() to find the number of days that the streak has lasted which might be more interesting than count() seeing as there are some days where there is no record.