An open item accounts payable system records each vendor invoice in a table row. A vendor may have MORE THAN ONE invoice in the table. The table structure for the table payables is:.

CREATE TABLE payables (
vendor-num int NOT NULL,
seq-num int IDENTITY, '**** auto-generated row number
vendor-name varchar(30) NOT NULL,
invoice-day char(2),
invoice-month char(2),
invoice-year char(2),
invoice-amt decimal (12,2),
amount-paid decimal(12,2),
check-num char(10),
paid-switch char(1), '**** "Y" = the invoice has been paid, "N" = the invoice has not been paid .
.
.

primary key (vendor-num, seq-num))

Write a active server page that allows invoices to be paid:

1. One the first pass, the asp program produces a list all vendors (i.e., every unique vendor-name) in the payables table (i.e., ONLY ONE ROW PER VENDOR in the report). This list is in alphabetical vendor-name order. Each name is a link. The link contains as part of the quertystring the vendor-num and a state maintenance variable. When the user clicks on a vendor name, the html page returns the vendor-num and state maintenance variable to the asp program.

2. On the second pass, the asp program creates a report with a list of all invoices that HAVE NOT BEEN PAID for the vendor-num requested. This list produces one row per invoice. The row contains: vendor-name, seq-num, invoice-amount, invoice month-day-year. The report is sorted in ascending date order (i.e., oldest first). The seq-num is a link. This link contains the vendor-num, seq-num and state-maintenance variable as part of its querystring. When the user clicks on a seq-num, the HTML page sends the querystring back to the asp program

3. On the third pass, the asp program returns the details of the specific invoice chosen in step two above (i.e., vendor-name, vendor-num, seq-num, invoice date, and invoice-amount). The program also returns: a text box that is labelled "Amount Paid"; a text box labelled "Check Number"; and a submit button. The user fills in the amount to be paid and the check-number and then clicks the submit button. A form is returned to the asp program that contains: vendor-name, vendor-num, seq-num, amount-paid, check-num and a state maintenance variable.

4. On the fourth pass, the asp program records the invoice payment. The form amounts are used to update the amount-paid and check-num fields and the paid-switch is set to "Y". The program should first:
   1. check the table for duplicate check numbers (i.e., assure that this check-num has not already been issued)
   2. check to be sure that the amount-paid equals the invoice-amount (i.e., no partial payments or overpayments are allowed)
   If either of these errors occurs::
   1. return an error message to the user that states the error problem (either duplicate check-num or wrong amount-paid)
   2. provide the user with all the data received on this pass (i.e., vendor-name, vendor-num, seq-num, amount-paid, check-num), two text boxes with amount-paid and check-num filled in (i.e., with values the user entered on the previous pass) and a submit button. This allows the user to correct their data and resubmit the form.
   else
   produce a page that tells the user that the invoice payment has been recorded OK.