Question

I’m looking for help to create a query, to solve the following problem:

Let’s imagine the row:

Name    StartDate   EndDate     Paid
James   10-10-2010  17-02-2011  860

And heres the schema for the table as requested:

payment_details (name VARCHAR(50) NOT NULL, 
                 start_date DATETIME NOT NULL, 
                 end_date DATETIME NOT NULL,
                 paidFLOAT NOT NULL)

Now I need a way to split this row up, so I can see what he pays every month, for his period, a query that returns:

Name    Year    Month   Paid
James   2010    10      172
James   2010    11      172
James   2010    12      172
James   2011    01      172
James   2011    02      172

There are lots of different customers with different StartDate/EndDate and amount payed, so the query has to handle this aswell. How can I do this in SQL (MS SQL Server 2005)?

Help will be much appreciated!

Answer 1

You probably need dates table, containig every date for reasonable period. Then you can join it to payments, calculating paid amount as total amount divided to period length in months.

select p.name, d.year, d.month, p.paid/(datediff(m, p.startdate, p.enddate) + 1)
from (
    select year(date) as year, month(date) as month, min(date) as monthbegin, max(date) as monthend
    from datestable
    group by year(date), month(date)
) d
left join payment_detail p on d.monthbegin<p.enddate and d.monthend>p.startdate

I hope I got join conditions right, feel free to correct (I’ve no possibility to test here).