>>So, when you send out the invoice, it can show something like:
>>

>>     Amount Due:  $100.00
>>     Amount if paid by (net 30 date):  $90.00
>>

>
>No sir,
>Amount due will be remain same in both cases, the customer pays or not.
>If he pays within 30 days then 10% of due amount will be added in his ledger through journal voucher.
Mehmood,
doi you make it a habit to consult every forum with the same question?
I found your question on Foxite, Tektips and now on this forum.
For your info, you are missing the forums:

https://social.msdn.microsoft.com/Forums/en-US/home?forum=visualfoxprogeneral
http://www.atoutfox.org/nntp.asp
http://www.fox4um.com/viewtopic.php?id=517
http://portal.dfpug.de/dfpug/
.....
And still your tables invoice has no relation to the other table, impossible to construct an reliable select statement.

Regards,
Koen