And once you know the basics, I strongly recommend "SQL Anti-Patterns" for a good guide for what not to do and why not (and what mitigating circumstances might make an otherwise bad choice OK (or simply the only available option)). I read it while considering myself experienced and found it to be a useful refresher. The style/tone is light and well organised by task/objective, so I suspect everyone down to a beginner will find it well worth their time perusing.
"I read it while considering myself experienced and found it to be a useful refresher."
I'll be honest and say I read it and found it terribly embarrassing yet comforting. Remember that dumb thing I did back in '96? (insert red face) Yeah I guess I'm not the only guy to learn that the hard way. That lack of deep experience is a significant danger of nosql designs. The folks doing that now, don't even see the icebergs that relational folks successfully dodged decades ago. Much better off being nostalgic about the olden days of steam engine trains than not even seeing the diesel-electric headlight at the end of the tunnel rushing toward you.
