What you need is a web developer.
Particularly a web developer with experience on on a LAMP (Linux, Apache,MySQL, PHP) platform.
It's possible a webmaster has these skills, the title webmaster ( like any job title) can be a bit vague. It usually means they are in general in charge of the overall operation of a website, The question is, does that website use PHP and SQL? Does he have a developer (in house or outsourced) to do the programing work.
Bottom line is you'll have to ask him. Maybe before telling him why you're asking ask him if he's made a LAMP based website utilizing PHP and MYSQL.
On the other hand, even if he is experienced, there are other complications that might come up ( doesn't deliver for some other reason, takes too long, misunderstanding about money) that could strain your relationship with your Friend. Maybe you should find someone else anyway.