SQL - Distribute Amount Between Dates

I'm trying to forecast an amount between two dates. The amount is evenly spread between the dates - see tables below for reference. Should (hopefully) be simple - any ideas?

The source table looks like this:

+-----------+---------------+---------------+------+--------------+----------------+
|  Project  |  Start Date   |   End Date    | Days | Total Budget | Budget Per Day |
+-----------+---------------+---------------+------+--------------+----------------+
| Project 1 | Jan. 01, 2017 | Apr. 11, 2017 |  100 |          100 |  1.00          |
| Project 2 | Feb. 05, 2017 | Apr. 06, 2017 |   60 |          200 |  3.33          |
| Project 3 | Feb. 03, 2017 | May. 03, 2017 |   89 |           50 |  0.56          |
| Project 4 | Jan. 01, 2017 | Aug. 04, 2017 |  215 |          300 |  1.40          |
+-----------+---------------+---------------+------+--------------+----------------+

The resulting table should look like this:

+-----------+---------------+--------+
|  Project  |      Day      | Budget |
+-----------+---------------+--------+
| Project 1 | Jan. 01, 2017 |  1.00  |
| Project 1 | Jan. 02, 2017 |  1.00  |
| Project 1 | Jan. 03, 2017 |  1.00  |
| Project 1 | Jan. 04, 2017 |  1.00  |
| Project 1 | Jan. 05, 2017 |  1.00  |
| …         | …             | …      |
+-----------+---------------+--------+

Side note: The goal is to then easily do different aggregations: by month, by year, etc. And eventually different distributions such as 10% of budget in first 10% of the days, etc. Any suggestions for how to best do this would be greatly appreciated.

Solution

Firstly, generate for yourself a Calendar table. They are extremely useful!

CREATE TABLE dbo.tCalendar(
    Date_Value DATE PRIMARY KEY NOT NULL,
    Year AS (DATEPART(YEAR, Date_Value)) PERSISTED,
    Month AS (DATEPART(MONTH, Date_Value)) PERSISTED,
    Day AS (DATEPART(DAY, Date_Value)) PERSISTED,
    Day_Of_Year AS (DATEPART(DY, Date_Value)) PERSISTED,
)

INSERT INTO dbo.tCalendar
SELECT *
FROM (
    SELECT DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY (SELECT 1)) - 1, '2000-01-01') AS d
    FROM        (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1))v(n)
    CROSS JOIN (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1))w(n)
    CROSS JOIN (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1))x(n)
    CROSS JOIN (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1))y(n)
) cal
WHERE cal.d <= '2027-12-31'

--SELECT * FROM  dbo.tCalendar

Now you can simply JOIN the calendar table to get the result you require:

CREATE TABLE #Project(
    Project VARCHAR(100) PRIMARY KEY NOT NULL,
    Start_Date DATE,
    End_Date DATE,
    Days AS (DATEDIFF(DAY, Start_Date,End_Date) + 1) PERSISTED,
    Total_Budget DECIMAL(19,2),
    Budget_Per_Day AS (CAST(Total_Budget / (DATEDIFF(DAY, Start_Date,End_Date) + 1) AS DECIMAL(19,2))) PERSISTED
)

INSERT INTO #Project (Project, Start_Date, End_Date, Total_Budget)
VALUES
('Project 1', '2017-01-01', '2017-04-10', 100),
('Project 2', '2017-02-05', '2017-04-05', 200),
('Project 3', '2017-02-03', '2017-05-02', 50),
('Project 4', '2017-01-01', '2017-08-03', 300)

SELECT *
FROM #Project

SELECT   p.Project
        ,cal.Date_Value
        ,p.Budget_Per_Day
FROM #Project p
    INNER JOIN dbo.tCalendar cal
        ON cal.Date_Value BETWEEN p.Start_Date AND p.End_Date

For more complex distributions, one solution is to have a table to store budget allocation by a date range, eg:

CREATE TABLE #Project_Budget_Range(
    Project VARCHAR(100) NOT NULL,
    Range_Start_Date DATE NOT NULL,
    Range_End_Date DATE NOT NULL,
    Range_Days AS (DATEDIFF(DAY, Range_Start_Date, Range_End_Date) + 1) PERSISTED,
    Budget_Allocation_Value DECIMAL(19,0) NULL,
    Budget_Allocation_Pct DECIMAL(9,4) NULL,
    PRIMARY KEY (Project, Range_Start_Date),
    -- End Date >= Start Date
    CONSTRAINT CK_Range_Start_End_Date CHECK (Range_End_Date>=Range_Start_Date),
    -- Either Budget_Allocation_Value or Budget_Allocation_Pct must have a value (but not both)
    CONSTRAINT CK_Allocation_Type CHECK (Budget_Allocation_Value + Budget_Allocation_Pct IS NULL AND COALESCE(Budget_Allocation_Value,Budget_Allocation_Pct) IS NOT NULL)
)

INSERT INTO #Project_Budget_Range
VALUES
('Project 1', '2017-01-01', '2017-01-31', NULL, 0.5),
('Project 1', '2017-02-01', '2017-02-28', 30, NULL),
('Project 1', '2017-03-01', '2017-04-10', 20, NULL)

SELECT * FROM #Project_Budget_Range

SELECT   p.Project
        ,p.Total_Budget
        ,cal.Date_Value
        ,CAST(COALESCE( 
            (b.Budget_Allocation_Pct * p.Total_Budget) / b.Range_Days, -- Allocation by Pct
            b.Budget_Allocation_Value / b.Range_Days -- Allocation by value
        ) AS DECIMAL(19,8)) AS Budget_Allocation
FROM #Project p
    INNER JOIN #Project_Budget_Range b
        ON p.Project = b.Project
    INNER JOIN dbo.tCalendar cal
        ON cal.Date_Value BETWEEN b.Range_Start_Date AND Range_End_Date
WHERE p.Project = 'Project 1'
;