Pseudo Columns

pseudo columns:
  • A Pseudo column behaves like a table column,but is not actually stored in the table.
  • you can select from Pseudo columns, but you cannot insert,update and delete their values.
  • pseudo columns are
      • Rowid
      • Rownum
      • currval
      • nextval
      • ORA_ROWSCN
      • Object_id
ROWID:
                For each row in the database the rowid returns the address of the row.

ROWNUM:
                Rownum returns sequence numbers when used in select statement.

ORA_ROWSCN:
                For each row ora_rowscn returns the conservative upper bound system change number (SCN) of the most recent change the row.
                         this is useful for determining approximately when a row was last updated.

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