SQL - Calculate number of days

Question

I am trying to calculate the number of days customers pay invoices either early or late.

select 
    a.Invoice, 
    datediff(day,InvoiceDate,JournalDate) as Days, 
    c.DueDays, 
    c.Description as Terms  

from 
    ArInvoice a 
    Inner Join ArInvoicePay b on a.Invoice = b.Invoice 
    Inner Join TblArTerms c on a.TermsCode = c.TermsCode

This is great for customers with a Date of Invoice term. The problem is for customers with for instance 60 days end of month . I am struggling to come up with a way using the InvoiceDate and using two other fields InvDayOfMonth = '31' and InvMonths = '2' to calculate the number of days.

In laymans terms I need to calculate the number of days from the InvoiceDate until 31 days, add this to the then multiplied InvMonth by 31.

Any pointers would be greatly appreciated.

Answer 1

SQL would look like this

SELECT 
dateadd(day,-1,
dateadd(month, 2, --Your variable here
--replace getdate with Invoice date, and figure out the 0+month part
convert(DATE, cast(Year(getdate()) as NVARCHAR) + '0'+cast(Month(getdate()) as NVARCHAR) + '01')))

Due to Your Comment the answer is simple then

SELECT 
dateadd(day,60,InvoiceDate) 
--replace 60 with the number You've already calculated