A pseudo-column is an Oracle assigned value (pseudo-field) used in the same context as an Oracle Database column, but not stored on disk. SQL and PL/SQL recognizes the following SQL pseudocolumns, which return specific data items: SYSDATE, SYSTIMESTAMP, ROWID, ROWNUM, UID, USER, LEVEL, CURRVAL, NEXTVAL, ORA_ROWSCN, etc.
1) Pseudo columns behave like a table column, but it is not actually stored in a table.
2) Upon pseudo columns only select statements can be implemented. Insert, delete,update cannot be implemented.
Currval, (can be used in set clause of an update, values clause of an insert)
Nextval, (can be used in set clause of an update, values clause of an insert)
Level, Rowid, Rownum.
Download here PDF on Pseudo column and functions in SQL
1) Pseudo columns behave like a table column, but it is not actually stored in a table.
2) Upon pseudo columns only select statements can be implemented. Insert, delete,update cannot be implemented.
Currval, (can be used in set clause of an update, values clause of an insert)
Nextval, (can be used in set clause of an update, values clause of an insert)
Level, Rowid, Rownum.
Download here PDF on Pseudo column and functions in SQL
SQL> SELECT sysdate, systimestamp FROM dual; SYSDATE SYSTIMESTAMP --------- ---------------------------------------- 13-DEC-07 13-DEC-07 10.02.31.956842 AM +02:00
SQL> select ename, ORA_ROWSCN, SCN_TO_TIMESTAMP(ORA_ROWSCN) from emp where empno=7369; ENAME ORA_ROWSCN SCN_TO_TIMESTAMP(ORA_ROWSCN) ---------- ---------- ---------------------------------------------------------------- SMITH 2113048 20/12/2008 16:59:51.000
