Invoice Management in a PHP Invoicing System

Continuing with the PHP Invoicing series, we will now concentrate on how to create, view and print an invoice. So let’s get started!

Create a new PHP document and save it as main.php. Refer to fig2 to see what the main page looks like. There are essentially three pages that deal with invoices:

• Allinv.php – Lists all invoices in the database.
  
• Unpaid.php – Lists all unpaid invoices.
  
• NewInvoice.php – Enables you to generate a new invoice.

There are also related pages that handle deleting and updating invoices.

Create a new document and save it as allinvoices.php. The page consists of both PHP and HTML code. Add the following code:

Code4  Allinv.php
<?
include "config.php";
$query_invoice = "SELECT *,DATE_FORMAT(inv_date,'%D %M %Y') as
idate,DATE_ADD(inv_date,INTERVAL 30 DAY) as duedate  FROM
invoices ORDER BY invno DESC";
$result_invoice = mysql_query($query_invoice);
$num_invoice = mysql_num_rows($result_invoice);
?>

This is a standard query that retrieves all the invoices in the database. The only things worth explaining are the DATE_FORMAT() and DATE_ADD() functions. The DATE_FORMAT function does exactly what the name implies: it formats the date that is stored in the way that you want it. The DATE_ADD() function adds a specified number of days (in this case it is 30) to the date column in the database.

I wanted the date formatted as dd mm yyyy which is displayed as, for example, "18^th June 2005." There are a variety of ways in which you can format a date. Check http://www.mysql.com/ for more details.  The 30 days that I’ve specified in the DATE_ADD() function will help us determine whether an invoice is overdue.

The number of rows returned by the query is stored in the "$num_invoices" variable. As you’ll see in a little while, it will be used to determine how many rows a table should have.