As pointed out by others here already, SQL may not be the optimal fit for every scenario at large scales but it will nearly always work at smaller scales, and I

As pointed out by others here already, SQL may not be the optimal fit for every scenario at large scales but it will nearly always work at smaller scales, and I can't imagine that you're already trying to write the next amazon.com. So in other words, start with SQL. There are three main free software SQL databases: MySQL, PostgreSQL, and SQLite. Don't use MySQL, it'll get you into a great deal of bad habits, is missing an ass-ton of useful features (the default engine doesn't even support transactions), and likes to corrupt data. It also has questionable licensing and is owned by Oracle (a commercial database vendor) which as you can imagine doesn't have a lot of incentive to improve it. SQLite is a very robust database that is great for read-mostly sites (like blogs) and for embedding into applications (Firefox for example). Its primary limitation is that there can only be one writer at a time. It is very easy to pick up and get going with since there's no persistent daemon, you just point it at a file and start writing. I'd recommend starting here. PostgreSQL is the more featureful database and supports hundreds of concurrent connections, locking, access control, etc. This is the real "workhorse" database you're likely to find in production at large sites that do make use of free-software RDBMS. Eventually you will need to use something more powerful than SQLite, and this is probably it.