MySQL site - great resource for syntax, code examples
My preferred flavor of SQL is MySQL. Why? It comes with the web host I use most frequently. I'm not a SQL whiz. I know just enough to get by. Industrial SQL gurus - you probably have a million reasons why MySQL isn't that great, but for modest applications and on-the-side-hobby needs, MySQL is just right. It's easy to use with PHP and is ... well, priced "just right".
Also their site is a great resource of syntax and examples. For example, if you wanted to know everything you could ever do with the SELECT statement, you'll be blown away by this page.