The MySQL site:
MySQL Developer Zone
One of the most important things of database development is understanding the concepts behind Database Normalization. This means setting up the proper structure of your tables and how they will work together to make your data retrieval as seemless as possible while minimizing data resources necessary to perform the output.
An intro to database normalization
Managing hierarchical data can be tricky, but once you get an understanding of how to approach it, you will find this an important tool in your database development.
Managing hierarchical data
Categories and Subcategories
a useful article written on the Adjacency List model.
Joe Celko's Trees and Hierarchies in SQL for Smarties
(I've found this to be a pretty involved book.)
MySQL Query Browser
if you are using PHP as well
(note, there are no comments on the designs, just the layouts)
SQL injection attacks:
result from unsanitized user input. The article below details one example of how this could be used to gain access to your data by outside users.
PHP and MySQL
An extensive tutorial
I found this tutorial to be pretty extensive and quite helpful.
(a quick and seemless way to integrate PHP, MySQL, Apache, PERL, PHPMYADMIN on Windows, Solaris, Linux, Mac OS). Note you won't learn how to tune your applications here, but if you are looking to get them set up quickly and jump right in, I personally have found this to be a good set-up on WinXP. Caveat, the discussion boards on the site are in German.
These allow you to dump in the code you are using for a query and print it out in a much neater form.
Instant SQL Formatter