Use of Oracle DUAL tables

DUAL table:
Dual enables the system table, whose owner is the sys user. Cannot be deleted.
All users can access it.
A dual table is also called a virtual table.
There is only one field in the dual table. This field makes dummy.

SQL> DESC DUAL;
Is the name empty? Type
-------------------------------------------------------------

DUMMY VARCHAR2 (1)

SQL> SELECT * FROM DUAL;

D
-
X

Dual tables are used to calculate expressions or test them.
For example, we want to view the current time.
We need to use the sysdate function.
Example:

SQL> SELECT SYSDATE FROM DUAL;

SYSDATE
----------
September 13-12-10

To get more detailed time, use the SYSTIMESTAMP Function
SQL> SELECT distinct imestamp FROM DUAL;

SYSTIMESTAMP
---------------------------------------------
-10 04.47.59.484000 PM +