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OCA Oracle Database 11g: SQL Fundamentals I Exam Guide (Exam 1Z0-051) by Roopesh Ramklass, John Watson

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CERTIFICATION OBJECTIVES
9.01    Describe the Set Operators
9.02    Use a Set Operator to Combine Multiple Queries into a Single Query
9.03    Control the Order of Rows Returned
  Image      Two-Minute Drill
Q&A   Self Test
 
Any SQL query can be described mathematically (relational algebra is the term used for this), but the use of set operators is what recalls school mathematics to many programmers. As your math curriculum may not have included set theory, following is a short summary.
 
All SELECT statements return a set of rows. The set operators ...

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