Good Source To Improve SQL Knowledge

Hi,

I've been working as a .NET developer for many years. However, my educational background isn't in IT at all, so I occasionally find that there are big gaps in my knowledge when I'm called on to do certain things.

My current role is the first one I've had where the efficiency of my database calls has needed to be top-notch. Most of my previous posts have been in building intranet functionality for medium-sized companies so it's just not been an issue and my fairly basic level of SQL knowledge has been enough to get me by.

However, I'm increasingly finding I'm needing to look stuff up, ask for help and so forth and I'm not at all sure that what I'm putting out is up to scratch. I have three main areas of concern:

1) The developers here seem to like doing a lot of the "work" of data sorting and manipulation in SQL whereas I'd previously have just grabbed the whole table and done the manipulation in .NET. I'm finding building my complex queries is just doing my head in - I'm just not used to "thinking" in the way that SQL requires which seems very different from procedural programming.

2) A lot gets said about properly indexing tables for maximum efficiency. I know what an index is and vaguely what it does, but the means of applying them to ensure the best performance is pretty much beyond me.

3) In the same manner I'm now having to worry a lot more about performance issues in my database design. I now the five normal forms and so on, but is there anything else here I need to do to maximise performance?

What I'm asking, really, is whether anyone can recommend a good source for SQL knowledge (book, site, whatever) that specifically focuses on my first problem - it'll teach me the proper way to structure my queries and think about them properly so that they don't look so damn impenetrable. It then needs to go on and address my other issues.

Any suggestions?