What is dual table in Oracle?

Dual:

   v DUAL is a table automatically created by oracle database along with the data dictionary.

   v Dual is the schema of the user sys but is accessible by the name DUAL to all users.

   v It has only one column, DUMMY, defined by varchar2(1), and contains one row with a value X.

     Select * from Dual;

DUMMY

X

   v Selecting from the dual table is useful for computing a constant expression with the select statement. Because Dual has only one row, the constant is returned only once.

Example: 1

Computation operation:

    Select 5+5 from Dual;

Output:

5+5

10

Example: 2

   Select (500*2*10.5)/100 result from Dual;

Output:

RESULT

105

Find the user:

          Select user from dual;

    Output:

USER

APPS

 Find current date:

       Select sysdate from dual;

How can you print string in the pyramid structure?

1. SELECT ROWNUM, SUBSTR(‘Oracle’, 1, rownum), SUBSTR(‘Oracle’, ROWNUM)

   FROM DUAL

   CONNECT BY LEVEL <= LENGTH (‘Oracle’);

Output:

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