It's actually an inseparable combination. If you've ever run a site or configured a server, probably you've heard of things like
LAMP (Linux, Apache, MySQL, PHP), LNMP/LEMP (replace Apache with Nginx), WAMP (replace Linux with Windows), WIMP (replace Linux with Windows and Apache with IIS server, both of which belong to Microsoft) and so on. It's an inseparable bundle: Linux/Windows is the operating system; Apache/Nginx (among others) is the webserver; MySQL (also MariaDB, MSSQL, PostgreSQL and others) is the database; and PHP (also Perl, Python and others) is the programming language in which web content is delivered.
The standard modus operandi is that a website's software engine―e.g. our forum, a WordPress blog, a Joomla homepage and so on―is coded in PHP, delivered through Apache webserver which runs on a Linux server and stores content―such as posts, comments, user data and the like―in a MySQL database. Things like Javascript and CSS serve mainly as enhancements. For example, when you post a quick reply, your post can immediately appear without having to reload the page to see it. That's an Ajax (within which Javascript is contained) feature. Whereas CSS mainly deals with aesthetics, such as all these different colours you see on this page.
If you're interested to know more, I'm sure all the terms I mentioned have Wikipedia entries. You can start from there.
The bottom line is that it's a bit tricky to answer a "did you use PHP, SQL or Javascript to code this site?" kind of question, because like most other robust websites, it's never just one and always mix of many.