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select type
,sum(quantity) as quantity
from (
select *
,count(chng) over(order by id) as grp
from (
select *
,case when type <> lag(type) over(order by id) then 1 end as chng
from t
) t
) t
group by grp, type
| type | quantity |
|---|---|
| buy | 10 |
| sell | 4 |
| buy | 3 |
| sell | 2 |