Subquery Transformations
As I explained in Chapter 7, I have used the term subquery throughout this book in an informal way to indicate either a set query block or any part of a SQL statement that begins with the keyword SELECT and that is not the main query block of a query. So, for example, an inline view or data dictionary view is considered to be a subquery for the purposes of discussion here.
We have already discussed subquery unnesting both in Chapter 11 and earlier in this chapter, so I won’t be revisiting that topic again. But we still have a lot of other transformations to cover. Let us get started by briefly revisiting simple view merging.
Simple View Merging
We have already seen countless examples of simple view merging in this book, ...
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