Postgres 13

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12 rows affected

SELECT
s.sales_date, 
s.country,
s.sales_volume,
f.fix_costs,

(CASE WHEN country IN ('NL') THEN 0
       
       /* Exclude NL from fixed_costs calculation */
       WHEN SUM(CASE WHEN country NOT IN ('NL') THEN sales_volume ELSE 0 END) OVER (PARTITION BY sales_date) > 0
       THEN ((f.fix_costs/ extract(day FROM (date_trunc('month', sales_date + INTERVAL '1 month') - INTERVAL '1 day'))) *
              sales_volume / 
              NULLIF(SUM(s.sales_volume) FILTER (WHERE s.country NOT IN ('NL'))  OVER (PARTITION BY s.sales_date), 0)
              )
              
        /* Divide fixed_cots equaly among countries in case of no sale*/      
        ELSE (f.fix_costs / extract(day FROM (date_trunc('month', sales_date + INTERVAL '1 month') - INTERVAL '1 day')))
              / SUM(CASE WHEN country NOT IN ('NL') THEN 1 ELSE 0 END) OVER (PARTITION by sales_date)
              
        END) AS imputed_fix_costs
        
FROM sales s

JOIN

(SELECT 
  (date_trunc('MONTH', sales_date)) AS month_ld,
  SUM(fix_costs) AS fix_costs
  FROM sales
  WHERE country = 'None'
  GROUP BY month_ld) f ON f.month_ld = date_trunc('month', s.sales_date)

WHERE country NOT IN ('None')
GROUP BY 1,2,3,4
ORDER BY 1;

sales_date	country	sales_volume	fix_costs	imputed_fix_costs
2020-01-03	DE	500	2000	37.950664136622386
2020-01-03	FR	350	2000	26.565464895635674
2020-01-03	NL	320	2000	0
2020-02-15	DE	0	5000	86.20689655172414
2020-02-15	FR	0	5000	86.20689655172414
2020-02-15	NL	0	5000	0
2020-03-27	DE	180	4000	20.19635343618513
2020-03-27	FR	970	4000	108.83590462833101
2020-03-27	NL	670	4000	0