MariaDB 10.3

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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", "2020-01-03", "500", "0"),
("NL", "2020-01-03", "320", "0"),
("FR", "2020-01-03", "350", "0"),
("None", "2020-01-30", "0", "2000"),

("DE", "2020-02-15", "700", "0"),
("NL", "2020-02-15", "420", "0"),
("FR", "2020-02-15", "180", "0"),
("None", "2020-02-29", "0", "5000"),

("DE", "2020-03-27", "180", "0"),
("NL", "2020-03-27", "670", "0"),
("FR", "2020-03-27", "970", "0"),
("None", "2020-03-31", "0", "4000");
SELECT 
sales_date, 
country, 
SUM(sales_volume),
SUM(fix_costs) / DAY(LAST_DAY(sales_date)) AS fix_cost_per_day
FROM sales
GROUP BY 1,2;


sales_date
country
SUM(sales_volume)
fix_cost_per_day


2020-01-03
DE
500
0.0000

2020-01-03
FR
350
0.0000

2020-01-03
NL
320
0.0000

2020-01-30
None
0
64.5161

2020-02-15
DE
700
0.0000

2020-02-15
FR
180
0.0000

2020-02-15
NL
420
0.0000

2020-02-29
None
0
172.4138

2020-03-27
DE
180
0.0000

2020-03-27
FR
970
0.0000

2020-03-27
NL
670
0.0000

2020-03-31
None
0
129.0323


SELECT sales_date, country, 
       SUM(sales_volume),
       SUM(fix_costs) / DAY(LAST_DAY(sales_date)) AS fix_cost_per_day,
       (SUM(SUM(fix_costs))  OVER (PARTITION BY yyyy, mm) / DAY(LAST_DAY(sales_date))) *
        (SUM(sales_volume) / SUM(SUM(sales_volume)) OVER (PARTITION BY yyyy, mm)) as allocated
FROM (SELECT s.*, YEAR(sales_date) as yyyy, MONTH(sales_date) as mm
      FROM sales s
     ) s
GROUP BY 1,2;


sales_date
country
SUM(sales_volume)
fix_cost_per_day
allocated


2020-01-03
DE
500
0.0000
27.57099529

2020-01-03
FR
350
0.0000
19.29969671

2020-01-03
NL
320
0.0000
17.64543697

2020-01-30
None
0
64.5161
0.00000000

2020-02-15
DE
700
0.0000
92.83819621

2020-02-15
FR
180
0.0000
23.87267897

2020-02-15
NL
420
0.0000
55.70291776

2020-02-29
None
0
172.4138
0.00000000

2020-03-27
DE
180
0.0000
12.76143200

2020-03-27
FR
970
0.0000
68.76993961

2020-03-27
NL
670
0.0000
47.50088619

2020-03-31
None
0
129.0323
0.00000000

sales_date	country	SUM(sales_volume)	fix_cost_per_day
2020-01-03	DE	500	0.0000
2020-01-03	FR	350	0.0000
2020-01-03	NL	320	0.0000
2020-01-30	None	0	64.5161
2020-02-15	DE	700	0.0000
2020-02-15	FR	180	0.0000
2020-02-15	NL	420	0.0000
2020-02-29	None	0	172.4138
2020-03-27	DE	180	0.0000
2020-03-27	FR	970	0.0000
2020-03-27	NL	670	0.0000
2020-03-31	None	0	129.0323

sales_date	country	SUM(sales_volume)	fix_cost_per_day	allocated
2020-01-03	DE	500	0.0000	27.57099529
2020-01-03	FR	350	0.0000	19.29969671
2020-01-03	NL	320	0.0000	17.64543697
2020-01-30	None	0	64.5161	0.00000000
2020-02-15	DE	700	0.0000	92.83819621
2020-02-15	FR	180	0.0000	23.87267897
2020-02-15	NL	420	0.0000	55.70291776
2020-02-29	None	0	172.4138	0.00000000
2020-03-27	DE	180	0.0000	12.76143200
2020-03-27	FR	970	0.0000	68.76993961
2020-03-27	NL	670	0.0000	47.50088619
2020-03-31	None	0	129.0323	0.00000000