Pseudocolumn
Encyclopedia
A Pseudocolumn is a "column" that yields a value when selected, but which is not an actual column of the table. An example is RowID or SysDate. It is often used in combination with the DUAL table
DUAL table
The DUAL table is a special one-row table present by default in all Oracle database installations. It is suitable for use in selecting a pseudocolumn such as SYSDATE or USER.The table has a single VARCHAR2 column called DUMMY that has a value of 'X'....