MySQL - Count Rows between two values in a Column repeatedly - mysql

Question

I have a table like so
id | status | data | date
----|---------|--------|-------
1 | START | a4c | Jan 1
2 | WORKING | 2w3 | Dec 29
3 | WORKING | 2d3 | Dec 29
4 | WORKING | 3ew | Dec 26
5 | WORKING | 5r5 | Dec 23
6 | START | 2q3 | Dec 22
7 | WORKING | 32w | Dec 20
8 | WORKING | 9k5 | Dec 10
and so on...
What I am trying to do, is to get the number of 'WORKING' rows between two 'START' i.e.
id | status | count | date
----|---------|--------|-------
1 | START | 4 | Jan 1
6 | START | 2 | Dec 22
and so on ...
I am using MySql 5.7.28.
Highly appreciate any help/suggestion!

Answer 1

date is unusable in the example, try using id as an ordering column instead
select id, status,
(select count(*)
from mytable t2
where t2.id > t.id and t2.status='WORKING'
and not exists (select 1
from mytable t3
where t3.id > t.id and t3.id < t2.id and status='START')
) count,
date
from mytable t
where status='START';
Fiddle

Answer 2

Assuming id is safe then you can do this by finding the next id for each block (and assigning some dummy values) then grouping by next id
drop table if exists t;
create table t
(id int,status varchar(20), data varchar(3),date varchar(10));
insert into t values
( 1 , 'START' , 'a4c' , 'Jan 1'),
( 2 , 'WORKING' , '2w3' , 'Dec 29'),
( 3 , 'WORKING' , '2d3' , 'Dec 29'),
( 4 , 'WORKING' , '3ew' , 'Dec 26'),
( 5 , 'WORKING' , '5r5' , 'Dec 23'),
( 6 , 'START' , '2q3' , 'Dec 22'),
( 7 , 'WORKING' , '32w' , 'Dec 20'),
( 8 , 'WORKING' , '9k5' , 'Dec 10');
SELECT MIN(ID) ID,
'START' STATUS,
SUM(CASE WHEN STATUS <> 'START' THEN 1 ELSE 0 END) AS OBS,
Max(DATE) DATE
FROM
(
select t.*,
CASE WHEN STATUS = 'START' THEN DATE ELSE '' END AS DT,
COALESCE(
(select t1.id from t t1 where t1.STATUS = 'START' and t1.id > t.id ORDER BY T1.ID limit 1)
,99999) NEXTID
from t
) S
GROUP BY NEXTID;
+------+--------+------+--------+
| ID | STATUS | OBS | DATE |
+------+--------+------+--------+
| 1 | START | 4 | Jan 1 |
| 6 | START | 2 | Dec 22 |
+------+--------+------+--------+
2 rows in set (0.00 sec)

Answer 3

This is a form of gaps-and-islands problem -- which is simpler in MySQL 8+ using window functions.
In older versions, probably the most efficient method is to accumulate a count of starts to define groupings for the rows. You can do this using variables and then aggregate:
select min(id) as id, 'START' as status, sum(status = 'WORKING') as num_working, max(date) as date
from (select t.*, (#s := #s + (t.status = 'START')) as grp
from (select t.* from t order by id asc) t cross join
(select #s := 0) params
) t
group by grp
order by min(id);
Here is a db<>fiddle.

Answer 4

SELECT id, status, `count`, `date`
FROM ( SELECT #count `count`,
id,
status,
`date`,
#count:=(#status=status)*#count+1,
#status:=status
FROM test,
( SELECT #count:=0, #status:='' ) init_vars
ORDER BY id DESC
) calculations
WHERE status='START'
ORDER BY id
> Since I am still in design/development I can move to MySQL 8 if that makes it easier for this logic? Any idea how this could be done with Windows functions? – N0000B
WITH cte AS ( SELECT id,
status,
`date`,
SUM(status='WORKING') OVER (ORDER BY id DESC) workings
FROM test
ORDER BY id )
SELECT id,
status,
workings - COALESCE(LEAD(workings) OVER (ORDER BY id), 0) `count`,
`date`
FROM cte
WHERE status='START'
ORDER BY id
fiddle