Dummy tables in oracle database

[Norse]

Hello ,

I want to ask something regarding the dummy tables of oracle database,It always contains some rich information but not getting from where it is being processed and can a user control on this table and make some operation means updation and all. Please tell me the procedure how it processed in the database environment.

Thanks .

[Praetor]

The Dummy tables :

The dummy table is database management system provided table which is created with the data dictionary during the installation of oracle database and provide some intellectual synchronize information.

it has only one row and column and the name of column is "Dummy" and the value of record "X" always.

SQL> desc dual
 Name                    Null?    Type
 ----------------------- -------- ----------------
 DUMMY                            VARCHAR2(1)

SQL> select * from dual;

D
-
X

[Katty]

The pseudo column :

The Pseudo Column is Oracle assigned value used same as the normal columns of database tables.It is not stored on the disk.The SQL and PL/SQL catch it up below Pseudo columns like :

SYSDATE, SYSTIMESTAMP, ROWID, ROWNUM, UID, USER, LEVEL, CURRVAL, NEXTVAL, ORA_ROWSCN, etc.

These are not actually the columns but it behaves like columns but you cannot perform the insertion, updation or deletion from a pseudo column.

[kelfro]

The SYSDATE and SYSTIMESTAMP :

The SYSDATE and SYSTIMESTAMP are most important pseudo columns to find the current date and time of the system and database using different formats :

SQL> SELECT sysdate, systimestamp FROM dual;
SYSDATE   SYSTIMESTAMP
--------- ----------------------------------------
13-DEC-07 13-DEC-07 10.02.31.956842 AM +02:00

[Zecho]

The UID and USER :

The UID and USER columns is used to view the list of database user. which is executed by only DBA and privileged user of database. It takes the following form :

SQL> SELECT uid, user FROM dual;
       UID  USER
----------  ------------------------------
        20   MARRY