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Lesson 1

Introduction to the Oracle SELECT Statement and SQL Extensions

This course assumes that you are familiar enough with SQL to write basic queries, including queries that take advantage of these SQL features:
  1. Joining two or more tables
  2. Grouping and summarizing data
  3. Using sub-queries
This module covers some advanced SQL features, such as hierarchy queries and combining multiple queries with the UNION command. In addition, you will try out some query features that are exclusive to Oracle, such as the use of pseudocolumns.
A pseudocolumn is a special column generated when Oracle executes the query. There are a number of pseudocolumns, as you will see in this module.
Pseudocolumn: A pseudocolumn is data that Oracle makes available to you when it executes SQL commands.
These are created for convenience. For example, the Oracle user name that is executing the SQL is contained in the pseudocolumn called USER.

Module Objectives

By the end of this module, you will know how to:
  1. Use a variety of operators and conditions to write a query
  2. Write a query using the CONNECT BY feature
  3. Compare the INTERSECT, MINUS, and UNION commands
  4. Correctly place the HAVING DISTINCT or UNIQUE clauses in two queries
  5. Identify the uses of various pseudocolumns
The next lesson discusses operators and conditions that are not usually covered in introductory SQL courses.