Aktualisiert: Antwort gemäß Kommentar korrigiert.
Zeilen können nach Bedarf so gruppiert werden:
-- leave only first rows of each group and substitute col2 with a sum.
select
dateno,
col1,
group_sum as col2
from (
-- Get sum of col2 for each bucket
select
dateno,
col1,
is_start,
sum(col2) over (partition by bucket_number) group_sum
from (
-- divide rows into buckets based on previous col1 change count
select
dateno, col1, col2, is_start,
sum(is_start) over(order by dateno rows unbounded preceding) bucket_number
from (
-- mark rows with change of col1 value as start of new sequence
select
dateno, col1, col2,
decode (nvl(prev_col1, col1||'X'), col1, 0, 1) is_start
from (
-- determine for each row value of col1 in previous row.
select
dateno,
col1,
col2,
lag(col1) over (order by dateno) prev_col1
from t
)
)
)
)
where is_start = 1
order by dateno
Beispiel bei SQLFiddle
