Can I use SQL to plot actual dates based on schedule information? - sql

Question

If I have a table containing schedule information that implies particular dates, is there a SQL statement that can be written to convert that information into actual rows, using some sort of CROSS JOIN, perhaps?
Consider a payment schedule table with these columns:
StartDate - the date the schedule begins (1st payment is due on this date)
Term - the length in months of the schedule
Frequency - the number of months between recurrences
PaymentAmt - the payment amount :-)
SchedID StartDate Term Frequency PaymentAmt
-------------------------------------------------
1 05-Jan-2003 48 12 1000.00
2 20-Dec-2008 42 6 25.00
Is there a single SQL statement to allow me to go from the above to the following?
Running
SchedID Payment Due Expected
Num Date Total
--------------------------------------
1 1 05-Jan-2003 1000.00
1 2 05-Jan-2004 2000.00
1 3 05-Jan-2005 3000.00
1 4 05-Jan-2006 4000.00
1 5 05-Jan-2007 5000.00
2 1 20-Dec-2008 25.00
2 2 20-Jun-2009 50.00
2 3 20-Dec-2009 75.00
2 4 20-Jun-2010 100.00
2 5 20-Dec-2010 125.00
2 6 20-Jun-2011 150.00
2 7 20-Dec-2011 175.00
I'm using MS SQL Server 2005 (no hope for an upgrade soon) and I can already do this using a table variable and while loop, but it seemed like some sort of CROSS JOIN would apply but I don't know how that might work.
Your thoughts are appreciated.
EDIT: I'm actually using SQL Server 2005 though I initially said 2000. We aren't quite as backwards as I thought. Sorry.

Answer 1

I cannot test the code right now, so take it with a pinch of salt, but I think that something looking more or less like the following should answer the question:
with q(SchedId, PaymentNum, DueDate, RunningExpectedTotal) as
(select SchedId,
1 as PaymentNum,
StartDate as DueDate,
PaymentAmt as RunningExpectedTotal
from PaymentScheduleTable
union all
select q.SchedId,
1 + q.PaymentNum as PaymentNum,
DATEADD(month, s.Frequency, q.DueDate) as DueDate,
q.RunningExpectedTotal + s.PaymentAmt as RunningExpectedTotal
from q
inner join PaymentScheduleTable s
on s.SchedId = q.SchedId
where q.PaymentNum <= s.Term / s.Frequency)
select *
from q
order by SchedId, PaymentNum

Answer 2

Try using a table of integers (or better this: http://www.sql-server-helper.com/functions/integer-table.aspx) and a little date math, e..g. start + int * freq

Answer 3

I've used table-valued functions to achieve a similar result. Basically the same as using a table variable I know, but I remember being really pleased with the design.
The usage ends up reading very well, in my opinion:
/* assumes #startdate and #enddate schedule limits */
SELECT
p.paymentid,
ps.paymentnum,
ps.duedate,
ps.ret
FROM
payment p,
dbo.FUNC_get_payment_schedule(p.paymentid, #startdate, #enddate) ps
ORDER BY p.paymentid, ps.paymentnum

Answer 4

A typical solution is to use a Calendar table. You can expand it to fit your own needs, but it would look something like:
CREATE TABLE Calendar
(
calendar_date DATETIME NOT NULL,
is_holiday BIT NOT NULL DEFAULT(0),
CONSTRAINT PK_Calendar PRIMARY KEY CLUSTERED calendar_date
)
In addition to the is_holiday you can add other columns that are relevant for you. You can write a script to populate the table up through the next 10 or 100 or 1000 years and you should be all set. It makes queries like that one that you're trying to do much simpler and can give you additional functionality.