text: XPath & XQuery Tutorial for SQL Pros - Altova Blog
  Altova has a comprehensive, free training library which covers XPath and XQuery. I found that I could get a strong understanding of both of these query languages simply by reading through this training documentation and applying the basic concepts to sample XML files included with XMLSpy. I found it quite amazing how intuitive it was to instantly query massive XML files using just XPath. As I started producing more advanced use cases, though, I began to understand that the queries built using XQuery were almost always much more concise and easier to read/debug.
  MobileTogether includes a sample app called MyCar. This app demonstrates how to query a user about his or her dream car. The data is provided by a set of parameters defined within a database; it was ideal to work with as it contained many records which each had several data points. The dataset itself is provided as an MDB file which I opened with DatabaseSpy and exported to XML. I modified the exported file, changing a few of the fields to improve the readability of the queries I would produce.
  Below is a link containing all the sample queries and datasets which were used in the video. Grab a free trial of XMLSpy if you would like to experiment with them in the built-in XPath / XQuery editing window.