Pseudocolumns in Oracle

The word pseudo means flase. Pseudocolumn means false column which indicate the column is not stored within a table but they behaves as they are table columns.

You can only do select operation on pseudocolumns but you can't do insert, update, or delete their values.

You can compare pseudocolumn to a function which takes no argument.

The difference between pseudocolumn and function without argument is pseudocolumns typically return a different value for each row but functions without arguments typically return the same value for every row in the result set.

Based on the functions pseudocolumn can be divided into several types.

1)Hierarchical Query Pseudocolumns: Discussed in
2)Sequence Pseudocolumns: Discussed in
3)Version Query Pseudocolumns: Discussed in http://arjudba.blogspot.com/2008/07/version-query-pseudocolumns.html
4)COLUMN_VALUE Pseudocolumn: Discussed in
5)OBJECT_ID Pseudocolumn: Discussed in
6)OBJECT_VALUE Pseudocolumn: Discussed in
7)ORA_ROWSCN Pseudocolumn: Discussed in http://arjudba.blogspot.com/2008/07/can-i-get-idea-when-row-is-created.html
8)ROWID Pseudocolumn: Discussed in
9)ROWNUM Pseudocolumn: Discussed in http://arjudba.blogspot.com/2008/07/rownum-pseudocolumn-in-oracle.html
10)XMLDATA Pseudocolumn: Discussed in