SQL - creating a list of custom dates between two dates - sql

Question

I am having trouble compiling a query than can do the following:
I have a table which has a startDate and endDate [tblPayments]
I have a column which stores a specific paymentDay [tblPayments]
Data
paymentID startDate endDate paymentDay
1 2016-01-01 2016-12-31 25
2 2015-06-01 2016-06-30 16
I am trying to generate a SELECT query which will split this specific table into separate lines based on the amount of months between these two dates, and set the paymentDay as the day for these queries
Example Output
paymentID expectedDate
1 2016-01-25
1 2016-02-25
1 2016-03-25
1 2016-04-25
1 2016-05-25
1 2016-06-25
1 2016-07-25
1 2016-08-25
1 2016-09-25
1 2016-10-25
1 2016-11-25
1 2016-12-25
2 2015-06-16
2 2015-07-16
2 2015-08-16
2 2015-09-16
2 2015-10-16
2 2015-11-16
2 2015-12-16
2 2016-01-16
2 2016-02-16
2 2016-03-16
2 2016-04-16
2 2016-05-16
I have found a query which will select the months between these dates but its adapting it to my table above, and multiple startDates and endDates I am struggling with
spliting the months
declare #start DATE = '2015-01-01'
declare #end DATE = '2015-12-31'
;with months (date)
AS
(
SELECT #start
UNION ALL
SELECT DATEADD(MM,1,date)
from months
where DATEADD(MM,1,date)<=#end
)
select Datename(MM,date) from months
This query is limited to just one startDate and endDate, so I haven't expanded it to change the DAY of the date.

Answer 1

Use a date table and a simple inner join
DECLARE #tblPayments table (paymentID int identity(1,1), startDate date, endDate date, paymentDay int)
INSERT #tblPayments VALUES
('2016-01-01', '2016-12-31', 25),
('2015-06-01', '2016-06-30', 16)
;WITH dates AS -- Build date within the range of startDate and endDate
(
SELECT MIN(startDate) AS Value, MAX(endDate) AS MaxDate FROM #tblPayments
UNION ALL
SELECT DATEADD(DAY, 1, Value), MaxDate
FROM dates WHERE DATEADD(DAY, 1, Value) <= MaxDate
)
SELECT pay.paymentID, dates.Value AS expectedDate
FROM
#tblPayments pay
INNER JOIN dates ON
dates.Value BETWEEN pay.startDate AND pay.endDate
AND DAY(dates.Value) = paymentDay
OPTION (maxrecursion 0)

Answer 2

I would create an in memory calendar table and then perform a simple query by joining to that:
-- Create a table with all the dates between the min and max dates in the
-- data table
DECLARE #Calendar TABLE
(
[CalendarDate] DATETIME
)
DECLARE #StartDate DATETIME
DECLARE #EndDate DATETIME
SELECT #StartDate = MIN(startdate), #EndDate = MAX(enddate) FROM YourDataTable
WHILE #StartDate <= #EndDate
BEGIN
INSERT INTO #Calendar (CalendarDate)
SELECT #StartDate
SET #StartDate = DATEADD(dd, 1, #StartDate)
END
-- Join to return only dates between the start and end date that match the Payment Day
SELECT D.PaymentId, C.CalendarDate FROM YourDataTable D
INNER JOIN #Calendar C ON C.CalendarDate BETWEEN D.StartDate AND D.EndDate
AND DATEPART(day, C.CalendarDate) = D.PaymentDay