User475983607 posted
I suggest that you redesign the schema and add a date field then you can simply use the the between clause. The way the table is currently designed you'll need to convert the month and year field to a date using an SQL Date function like
DATEFROMPARTS.
SELECT SUM(Amount)
FROM theTable
WHERE DATEFROMPARTS(Year, Month, 1) BETWEEN DATEFROMPARTS(2015, 4, 1) AND DATEFROMPARTS(2015, 9, 1)
I imagine you'll pass the start and end dates to the script. At this point is not not clear how you get the end date.