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Chapter 27. Subsets

Chapter 27. Subsets

I AM DEFINING SUBSET operations as queries, which extract a particular subset from a given set, as opposed to set operations, which work among sets. The obvious way to extract a subset from a table is just to use a WHERE clause, which will pull out the rows that meet that criterion. But not all the subsets we want are easily defined by such a simple predicate. This chapter is a collection of tricks for constructing useful, but not obvious, subsets from a table.


  

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