What did "SET UNUSED COLUMN" do in Oracle? Just a Guess.
This command is used to quickly remove a column from a table with reorganize all the blocks, And you could do the blocks reorganization when system is free. I noticed the problem when someone set unused a column by mistake and asking "Can I rollback the operation when no backup available?". Let's start with the following example:
SQL> DESC T_FID
Name Null? Type
----------------------- -------- -------
COL1 NUMBER
COL2 NUMBER
COL3 NUMBER
SQL> ALTER TABLE T_FID SET UNUSED (COL3);
Table altered.
SQL> alter system checkpoint;
System altered.
Then you could query the COL$ directly (Columns: COL#, SEGCOL# and NAME), what's the new values for this columns? Here I will use AUL/MyDUL's DESCRIBE command to display the table structure after the operation.
