Update table records with accumulated result - sql

Question

Lets say I have a table Tbl (Represents simple timelogs for work made on different customers)
Five columns
Id: int
TimeUse: float
IdCustomer: int
Created: DateTime
TimeCalc: float
I have a number of records in this table, (TimeCalc is initialized to value = 0)
What I want my SQL to do is:
when TimeUse for all foregoing records on a specific customer accumulates to a value < 10 then the value in TimeCalc should be 0
when TimeUse for all foregoing records on a specific customer accumulates to a value >= 10 then the value in TimeCalc should be = TimeUse for the record...
I have messed around with Case routines with subqueries, but can't get it working.
BEFORE
Id TimeUse IdCustomer Created TimeCalc
1 2 1 14/09/09 0
2 5 2 14/09/10 0
3 2 1 14/09/11 0
4 5 2 14/09/12 0
5 4 1 14/09/13 0
6 2 2 14/09/14 0
7 4 1 14/09/15 0
8 1 1 14/09/16 0
9 3 2 14/09/17 0
10 2 1 14/09/18 0
11 4 2 14/09/19 0
AFTER
Id TimeUse IdCustomer Created TimeCalc
1 2 1 14/09/09 0
2 5 2 14/09/10 0
3 2 1 14/09/11 0
4 5 2 14/09/12 0
5 4 1 14/09/13 0
6 2 2 14/09/14 2
7 4 1 14/09/15 0
8 1 1 14/09/16 1
9 3 2 14/09/17 3
10 2 1 14/09/18 2
11 4 2 14/09/19 4
Can this be solved in an SQL update?

Answer 1

In SQL Server 2012+, you can do this with a cumulative sum:
select Id, TimeUse, IdCustomer, Created,
(case when sum(timeuse) over (partition by idcustomer order by id) < 10 then 0
else timeuse
end) as timecalc
from table t;
You can do the same thing in earlier versions using outer apply or a subquery.
If you want an update, just use a CTE:
with toupdate as (
select t.*,
(case when sum(timeuse) over (partition by idcustomer order by id) < 10 then 0
else timeuse
end) as new_timecalc
from table t
)
update toupdate
set timecalc = new_timecalc;
EDIT:
The following will work in any version of SQL Server:
with toupdate as (
select t.*,
(case when (select sum(t2.timeuse)
from table t2
where t2.idcustomer = t.idcustomer and
t2.id <= t.id
) < 10 then 0
else timeuse
end) as new_timecalc
from table t
)
update toupdate
set timecalc = new_timecalc;