Unusual Query Types
In this chapter:
What is a composite query and what are set operators?
What is a hierarchical query?
What are versions queries and what is flashback?
What are parallel queries?
Unusual query types are detailed in this chapter because they may be rarely used. On the other hand, certain types of queries do not really belong in previous chapters because they are either so obscure or just too complicated, until now. We begin with composite queries.
So what is a composite query? A composite query is simply a composite or concatenation of two queries. Special set operators are used to concatenate the results of two separate queries. There are certain restrictions, such as: both SELECT column sets in the ...