14.3. Joins, reporting queries, and subselects
It's difficult to categorize some queries as advanced and others as basic. Clearly, the queries we've shown you in the previous sections of this chapter aren't going to get you far.
At the least you also need to know how joins work. The ability to arbitrarily join data is one of the fundamental strengths of relational data access. Joining data is also the basic operation that enables you to fetch several associated objects and collections in a single query. We now show you how basic join operations work and how you use them to write a dynamic fetching strategy.
Other techniques we'd consider advanced include nesting of statements with subselects and report queries that aggregate and group results ...
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