SQL Count Consecutive Rows - sql

Question

I have a SQL table that I need to count the rows with 0 turnover, but the challenge is they resets. I only need the number of consecutive rows since it last generated any turnover.
Source data (it has a lot of different ID, just using 442 and 4500 in this case):
ID |Date | T/O |
442 |2019-12-31 | 0 |
442 |2020-01-01 |200.00|
442 |2020-01-02 | 0 |
442 |2020-02-06 | 0 |
442 |2020-02-07 | 0 |
442 |2020-02-08 | 0 |
442 |2020-02-09 |150.00|
442 |2020-02-10 | 0 |
442 |2020-02-11 | 0 |
442 |2020-02-15 | 0 |
4500 |2020-01-01 | 0 |
Intended results:
442 | 3 |
4500 | 1 |
I thought of using LAG(), but the number of rows between turnover generated can vary significantly. Sometimes it can be even 30+ rows.

Answer 1

SELECT id, COUNT(*) as [result]
FROM SourceData sd1
WHERE t_o=0
AND NOT EXISTS (SELECT 1
FROM SourceData sd2
WHERE sd1.id=sd2.id AND t_o != 0 AND sd2.[Date] > sd1.[Date])
GROUP BY id
DEMO

Answer 2

First we can get the last non-zero date for each id.
select id, max(date) as date
from example
where t_o > 0
group by id
This will not show a value for 4500 because it lacks a non-zero value.
Then we can use this to select and group only the values after those dates, or all rows if there was no non-zero date for an id.
with last_to as(
select id, max(date) as date
from example
where t_o > 0
group by id
)
select example.id, count(example.t_o)
from example
-- Use a left join to get all ids in example,
-- even those missing from last_to.
left join last_to on last_to.id = example.id
-- Account for the lack of a last_to row
-- if the ID has no non-zero values.
where last_to.date is null
or example.date > last_to.date
group by example.id
Demonstration.