Explain what is a DUAL table, where is it stored, and what is it useful for? Give an example of its use.

Question

What will be an ideal response?

Answer 1

A DUAL is a table with one column called DUMMY and contains one row with
a value 'X'. It is automatically created by Oracle along with the data dictionary.
DUAL is stored in the schema of the user SYS, but is accessible by the name
DUAL to all users.
DUAL is useful for computing a constant expression with the SELECT
statement. Because DUAL has only one row, the constant is returned only once.
e.g. SELECT LENGTH ('My String') FROM DUAL;