MySQL 8.0

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CREATE TABLE sales (
    id int auto_increment primary key,
    country VARCHAR(255),
    sales_date DATE,
    sales_volume INT,
    fix_costs INT
);
INSERT INTO sales
(country, sales_date, sales_volume, fix_costs
)
VALUES 

("DE", "2020-12-01", "500", "0"),
("NL", "2020-12-01", "320", "0"),
("FR", "2020-12-01", "350", "0"),

("DE", "2020-12-02", "700", "0"),
("NL", "2020-12-02", "420", "0"),
("FR", "2020-12-02", "180", "0"),

("DE", "2020-12-03", "0", "0"),
("NL", "2020-12-03", "0", "0"),
("FR", "2020-12-03", "0", "0")
select *
from sales


id
country
sales_date
sales_volume
fix_costs


1
DE
2020-12-01
500
0

2
NL
2020-12-01
320
0

3
FR
2020-12-01
350
0

4
DE
2020-12-02
700
0

5
NL
2020-12-02
420
0

6
FR
2020-12-02
180
0

7
DE
2020-12-03
0
0

8
NL
2020-12-03
0
0

9
FR
2020-12-03
0
0


    select s.*,
           (case when country = 'NL' then 0
                 else ((2000 / day(last_day(sales_date))) *
                       sales_volume / nullif(sum(case when country <> 'NL' then sales_volume end) over (partition by sales_date), 0)
                      )
            end) as imputed_fixed_costs
    from sales s
    order by id;


id
country
sales_date
sales_volume
fix_costs
imputed_fixed_costs


1
DE
2020-12-01
500
0
37.95066412

2
NL
2020-12-01
320
0
0.00000000

3
FR
2020-12-01
350
0
26.56546494

4
DE
2020-12-02
700
0
51.31964807

5
NL
2020-12-02
420
0
0.00000000

6
FR
2020-12-02
180
0
13.19648091

7
DE
2020-12-03
0
0
null

8
NL
2020-12-03
0
0
0.00000000

9
FR
2020-12-03
0
0
null


select s.*,
       (case when country = 'NL'
             then 0
             when sum(case when country <> 'NL' then sales_volume end) over (partition by sales_date) > 0
             then ((2000 / day(last_day(sales_date))) *
                   sales_volume / nullif(sum(case when country <> 'NL' then sales_volume end) over (partition by sales_date), 0)
                  )
             else (2000 / day(last_day(sales_date))) * 1 / sum(country <> 'NL') over (partition by sales_date)
        end) as imputed_fixed_costs
from sales s
order by id


id
country
sales_date
sales_volume
fix_costs
imputed_fixed_costs


1
DE
2020-12-01
500
0
37.95066412

2
NL
2020-12-01
320
0
0.00000000

3
FR
2020-12-01
350
0
26.56546494

4
DE
2020-12-02
700
0
51.31964807

5
NL
2020-12-02
420
0
0.00000000

6
FR
2020-12-02
180
0
13.19648091

7
DE
2020-12-03
0
0
32.25805000

8
NL
2020-12-03
0
0
0.00000000

9
FR
2020-12-03
0
0
32.25805000

id	country	sales_date	sales_volume
1	DE	2020-12-01	500
2	NL	2020-12-01	320
3	FR	2020-12-01	350
4	DE	2020-12-02	700
5	NL	2020-12-02	420
6	FR	2020-12-02	180
7	DE	2020-12-03	0
8	NL	2020-12-03	0
9	FR	2020-12-03	0

id	country	sales_date	sales_volume	imputed_fixed_costs
1	DE	2020-12-01	500	37.95066412
2	NL	2020-12-01	320	0.00000000
3	FR	2020-12-01	350	26.56546494
4	DE	2020-12-02	700	51.31964807
5	NL	2020-12-02	420	0.00000000
6	FR	2020-12-02	180	13.19648091
7	DE	2020-12-03	0	null
8	NL	2020-12-03	0	0.00000000
9	FR	2020-12-03	0	null