SO 62643683 - Consecutive days with negative balance, Sql Server

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CREATE TABLE T1
    ([ID] varchar(1), [Date] varchar(12), [Balance] int);
    
INSERT INTO T1
    ([ID], [Date], [Balance])
VALUES
    ('A', '20200620', 150),
    ('A', '20200621', -130),
    ('A', '20200621', -140),
    ('A', '20200621', -200),
    ('A', '20200622', 200),
    ('A', '20200622', 300),
    ('B', '20200621', 350),
    ('B', '20200621', 400),
    ('B', '20200621', -150),
    ('B', '20200622', -200),
    ('B', '20200622', -300),
    ('B', '20200623', -400),
    ('B', '20200623', -500)
;

with data as (
    select id, date,
        case when min(balance) >= 0 then 0 else 1 end as tally,
        sum(case when min(balance) >= 0 then 1 else 0 end)
            over (partition by id order by date) +
        datediff(day, min(date) over (partition by id), date) -
        row_number() over (partition by id order by date) + 1 as grp
    from t1
    group by id, date
)
select id, date,
    sum(tally) over (partition by id, grp, tally order by date) as running_consecutive_days
from data
order by id, date;

View schema
Execution time: 0,02 sec, rows selected: 6, rows affected: 13, absolute service time: 0,2 sec, absolute service time: 0,2 sec