Improving your SQL skills
Personally I've been using SQL long enough that while it might not flow from my fingers as it did previously with a bit of thinking it comes back fairly quickly. I tend to think of it like fitness, if you go to the gym regularly your fitness levels improve quickly, slack off and they drop back down almost as fast.
To keep my SQL skills "fit" I visit another sort of gym, the MySQL Forums, to be exact the Newbie forum. In that forum there are plenty of people offering you the chance of a mental work out at all skill levels, because of it's very nature there are all sorts of questions which often need a clever solution. While it’s a pain to most people the lack of support for sub-queries in MySQL 4.0 is great for a work out as it often makes you think a little harder about how to tackle a problem you might normally throw a sub-query at.
If you ever become too fit for the Newbie forum there are plenty of others, just like a gym has different equipment to work different areas of your body, the MySQL Forum has different sections to raise you SQL fitness levels further, the General and Performance being good ones to put mass on those SQL muscles.
The great thing about these questions is that during your normal working year you might never get to use some of the features needed to answer them, there is nothing worse that your boss dumping a set of reports requirements on your desk and having no idea how to even start constructing the SQL. But if you have been working out at the SQL gym you’re likely to have come across a few methods to get started.
So why not do what the government health departments keep telling us and spent 30 minutes a day in the gym.