PHP and MySQL complement each other to do with neither can do alone. PHP can collect data, and MySQL can in turn store the information. PHP can create dynamic calculations, and MySQL can provide it with the variables
it uses. PHP can create a shopping cart for your web store, but MySQL can then keep the data in a format PHP can use to create receipts on demand, show current order status, or even suggest other related products.
Although PHP and MySQL can each be used independently, when you put them together it opens up countless possibilities for your site. As the internet progresses, it becomes more and more necessary to deliver dynamic content to keep up with the demands of web surfers and their desire to have information instantly delivered to them online. By learning to use PHP and MySQL you can deliver this information to them on demand.