Уж не знаю, насколько распространена арифметика дат.
И совсем не хотел бы гонять такое по реальной базе.
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with x as (
select date'2017-02-01' dt, 1 status from dual union all
select date'2017-02-05', 2 from dual union all
select date'2017-02-07', 2 from dual union all
select date'2017-02-21', 3 from dual union all
select date'2017-02-24', 1 from dual union all
select date'2017-02-25', 3 from dual union all
select date'2017-02-28', 2 from dual union all
select date'2017-03-03', 1 from dual
)
---------------------------------------------------------
select status, sum(days_in_status) as days_in_status
from(
select x1.status
, coalesce(min(x2.dt), x1.dt+1) - x1.dt as days_in_status
from x x1 left join x x2 on x1.dt<x2.dt
group by x1.status, x1.dt
) group by status
order by status
