Need a sum on my current column

Question

On an Oracle database, I need to calculate something like this - on column my

id yr    m    v1  v2 v3 st my
1  2015  10   1   0  0  0  0
2  2015  10   0   0  2  1  4
3  2015  10   2   0  0  1  0
4  2015  10   0   1  0  1  0

When st=1, calculate 10 (total from m row) minus total in rows v1+v2+v3 (6) = 4. So, in the second row I will put 4 and in the third row, the total of 10 is reached and I will put 0. The same in the 4th row. So I need to calculate a sum on rows until the current row. Can I do this?

The sum on v1+v2+v3 is something like this:

(sum(v1+v2+v3) over (partition by yr)) 

How can I find out the sum for the row I calculate my so I won't get over my maximum sum from m?

Answer 1

If I understand this correctly, what you want to do is successively subtract the value of SUM(v1 + v2 + v3) OVER (PARTITION BY year) from m for each row where st is 1, until m is exhausted; once the result drops to zero or below, it should show just 0.

Since the subtracted value is the same, you could just enumerate all st=1 rows and subtract sum * row_number for each row, like this:

WITH calculated AS (
  SELECT
    mytable.*,
    m - SUM(v1 + v2 + v3) OVER (PARTITION BY yr)
      * ROW_NUMBER()      OVER (PARTITION BY yr, st ORDER BY id ASC) AS res
  FROM
    mytable
)
SELECT
  id,
  yr,
  m,
  v1,
  v2,
  v3,
  st,
  CASE WHEN st = 1 AND res > 0 THEN res ELSE 0 END AS my
FROM
  calculated
;

The above assumes that m is the same across all rows of a partition.