How to calculate moving sum with reset based on condition in teradata SQL? - sql

Question

I have this data and I want to sum the field USAGE_FLAG but reset when it drops to 0 or moves to a new ID keeping the dataset ordered by SU_ID and WEEK:
SU_ID WEEK USAGE_FLAG
100 1 0
100 2 7
100 3 7
100 4 0
101 1 0
101 2 7
101 3 0
101 4 7
102 1 7
102 2 7
102 3 7
102 4 0
So I want to create this table:
SU_ID WEEK USAGE_FLAG SUM
100 1 0 0
100 2 7 7
100 3 7 14
100 4 0 0
101 1 0 0
101 2 7 7
101 3 0 0
101 4 7 7
102 1 7 7
102 2 7 14
102 3 7 21
102 4 0 0
I have tried the MSUM() function using GROUP BY but it won't keep the order I want above. It groups the 7's and the week numbers together which I don't want.
Anyone know if this is possible to do? I'm using teradata

Answer 1

In standard SQL a running sum can be done using a windowing function:
select su_id,
week,
usage_flag,
sum(usage_flag) over (partition by su_id order by week) as running_sum
from the_table;
I know Teradata supports windowing functions, I just don't know whether it also supports an order by in the window definition.
Resetting the sum is a bit more complicated. You first need to create "group IDs" that change each time the usage_flag goes to 0. The following works in PostgreSQL, I don't know if this works in Teradata as well:
select su_id,
week,
usage_flag,
sum(usage_flag) over (partition by su_id, group_nr order by week) as running_sum
from (
select t1.*,
sum(group_flag) over (partition by su_id order by week) as group_nr
from (
select *,
case
when usage_flag = 0 then 1
else 0
end as group_flag
from the_table
) t1
) t2
order by su_id, week;

Answer 2

Try below code, with use of RESET function it is working fine.
select su_id,
week,
usage_flag,
SUM(usage_flag) OVER (
PARTITION BY su_id
ORDER BY week
RESET WHEN usage_flag < /* preceding row */ SUM(usage_flag) OVER (
PARTITION BY su_id ORDER BY week
ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING)
ROWS UNBOUNDED PRECEDING
)
from emp_su;

Answer 3

Please try below SQL:
select su_id,
week,
usage_flag,
SUM(usage_flag) OVER (PARTITION BY su_id ORDER BY week
RESET WHEN usage_flag = 0
ROWS UNBOUNDED PRECEDING
)
from emp_su;
Here RESET WHEN usage_flag = 0 will reset sum whenever sum usage_flag drops to 0