Syntax error in setting unused column I have a table named e_emp3 in Oracle with these fields among others:


FNAME VARCHAR2(20 BYTE)       
SAL   NUMBER(8,2)         
DEPTNO    NUMBER(4,0) 


I need to alter e_emp3 and set unused column(sal) with online keyword to stay dml operations for users on this table. I wrote this code:

alter table e_emp3 set unused(sal) online;


but I got the following error message 



Please help me what is problem? When I run this code without online keyword it succeeds. When I add online keyword it fails.
Once you mark a column unusued, there is no way back, just restore from backup.

Dropping Table Columns


  Removing Unused Columns
  
  The ALTER TABLE...DROP UNUSED COLUMNS statement is the only action
  allowed on unused columns. It physically removes unused columns from
  the table and reclaims disk space.