Learning to Query in Oracle XE - Example 3: Dual Tables
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Another of Oracle's very useful constructs is the Dual table. This is a table with just one column into which you can stuff your own value. Here is what you will get when you describe the Dual table.

 If you were to use a select query, Select 'hello' from dual, it would return 'Hello' in the Dummy column.

An example of using Dual

You could run a math function to be evaluated into dummy as shown in the next picture.

Summary

The SQL Command window of Oracle XE has is an extremely intuitive and user-friendly interface to run SQL, PL/SQL queries. The results of running a query against the database are provided in a single, tabbed window. The SavedSQL and history features provide links that will help refining and back tracking previously run queries.

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