Filter out rows from the final result, while still utilizing some of their values? - sql

Question

To give an example, let's say I have a view that returns the following result:
| id | foreignkey | value1 | value2 |
|----|------------|--------|--------|
| 1 | 500 | -100 | 0 |
| 2 | 500 | 900 | 15 |
| 3 | 500 | 570 | 25 |
| 4 | 999 | 100 | 57 |
| 5 | 999 | 150 | 0 |
The logic I'm trying to implement is as follows -
Filter out all rows that have value2 = 0.
But, for rows that have value2 = 0, I need to add it's value1 to the value1 of all other rows with the same foreign key where value2 != 0. If there are no other rows with the same foreign key, then rows with value2 = 0 simply get filtered out.
So in this example, I want the final result to be
| id | foreignkey | value1 | value2 |
|----|------------|--------|--------|
| 2 | 500 | 800 | 15 |
| 3 | 500 | 470 | 25 |
| 4 | 999 | 250 | 57 |
Any ideas? I was thinking something with group by might be possible but haven't been able to come up with a solution yet.

Answer 1

With SUM() window function:
select id, foreignkey, value1 + coalesce(total, 0) value1, value2
from (
select *,
sum(case when value2 = 0 then value1 end) over (partition by foreignkey) total
from tablename
) t
where value2 <> 0
See the demo.
Results:
> id | foreignkey | value1 | value2
> -: | ---------: | -----: | -----:
> 2 | 500 | 800 | 15
> 3 | 500 | 470 | 25
> 4 | 999 | 250 | 57

Answer 2

Hmmm . . . assuming that this doesn't filter out all rows, you can use window functions like this:
select id, foreignkey, value1, value2 + (case when seqnum = 1 then value2_0 else 0 end)
from (select t.*,
row_number() over (partition by foreignkey order by value1 desc) as seqnum,
sum(case when value1 = 0 then value2 end) over (partition by foreignkey) as value2_0
from t
) t
where value2 <> 0;

Answer 3

One way is to treat all zero rows as one group and all others as another group (based on foreignkey) and then simply join and add the values and finally select only the required ones:
;with cte as
(
select id, foreignkey, value1, value2,dense_rank() over (partition by foreignkey order by (case when value2 = 0 then 0 else 1 end)) as rn
from #t t1
)
,cte2 as
(
select t1.id, t1.foreignkey, t1.value1 + isnull(t2.value1,0) as value1, t1.value2
from cte t1
left join cte t2 on (t2.foreignkey = t1.foreignkey and t1.rn<> t2.rn)
)
select * from cte2
where value2 <> 0
Please find the db<>fiddle here.