SQL Server 2019

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CREATE TABLE Source([Source_id] int, [Description] varchar(3));
    
INSERT INTO Source ([Source_id], [Description]) VALUES
    (1, 'ABC'), (2, 'DEF'), (3, 'XYZ');
3 rows affected

CREATE TABLE Calc([Source_id] int, [date] date, [metric1] int, [metric2] int);
    
INSERT INTO Calc([Source_id], [date], [metric1], [metric2]) VALUES
    (1, '20201010', 2, 3),
    (2, '20201010', 4, 5),
    (3, '20201010', 6, 7),
    (1, '20201011', 8, 9),
    (2, '20201011', 10, 11),
    (3, '20201011', 12, 13),
    (1, '20201012', 14, 15),
    (2, '20201012', 16, 17),
    (3, '20201012', 18, 19);
9 rows affected

CREATE TABLE Factor([Date] date, [Factor] numeric(5, 2));
    
INSERT INTO Factor([Date], [Factor]) VALUES
    ('20201010', .3), ('20201011', .5), ('20201012', .7);
3 rows affected

WITH cte AS (SELECT '20201010' min_date, '20201012' max_date)
SELECT s.Description,
       ROUND(SUM(c.metric1 * c.metric2 * f.factor / (DATEDIFF(day, t.min_date, t.max_date) + 1)), 2) calculated_value
FROM cte t CROSS JOIN Source s 
LEFT JOIN Calc c ON c.Source_id = s.Source_id AND c.date BETWEEN t.min_date AND t.max_date
LEFT JOIN Factor f ON f.date = c.date
GROUP BY s.Source_id, s.Description


Description
calculated_value


ABC
61.6000000000000

DEF
83.8000000000000

XYZ
110.0000000000000