Is there any resource recommendations in general for getting past the basics of QGIS and going into the deep dark secrets?
Specifically in relation to expression coding for labeling, queries, etc.
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Underdark has composed some nice examples for labeling expressions:
Here are some helpful links for querying:
If you are interested in coding then you can start with this resource:
a nice blog with good QGIS tutorials : http://woostuff.wordpress.com/