title: What is the best online SQL tutorial for learning to write complex reporting queries?
body: <p>My SQL skills are rather limited and since I find myself working with a DB (Oracle) a lot lately I would like to get beyond the basic select statements.</p>
  
  <p>I want to write queries that do things like get data from multiple tables, sum quantities, compare dates, group, filter etc.</p>
  
  <p>What sites can you recommend for getting SQL reporting skills to a more advanced level?</p>