What is "dual"?

I am learning PL/SQL and have looked through two books, google searched, and 10 pages of DEJA and haven't found a good explanation...

My book gives the example:
SELECT 'COLUMBUS'
  INTO v_city
  FROM dual;

There is no "dual" table though, so I'm curious just what this is. I would think it would be "FROM zipcode" which is the table that contains the city information.

Insight appreciated. Thanks!

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http://www.deja.com/ Received on Sat Jan 13 2001 - 17:14:56 CST