Now to be picky. SQL is a language which has been around since the 70;s invented by Codd and Date. There are ANSI SQL standards and if you write to these then the application should run with many Relational databases.
The database manager (and MYSQL is one of many) implements the SQL language to some degree or other.
The commerical database manager leaders are Oracle and DB2. Oh and Microsoft have one as well I believe. Free databases like MYSQL have/are only just implementing support for some of these standards.
If you go to the MYSQL site, there is a 1700 page manual on the language, installing, the syntax, the commands, and LOADS of examples.
When I first started writing my site and using MYSQL I soon had problems, quite a few features of the ANSII SQL language were not implemented. This would only be a problem for those who use the commercial products on a daily basis. That may have changed, I have upgraded to a newer version, but not gone back to my code.
My own website is driven totally with SQL. The only pages which are not SQL driven are the links pages. The idea being you can search on the data with various parameters, escort location, escort hair colour, escort services. All this information is captured and stored into the database tables when the escort creates her profile.