SQL & PL/SQL :: DDL Trigger After Alter Table

I created a DDL trigger which manipulates columns of a table after an "alter table" statement.

For us this was all the time
"alter table XXX add NEW_COL varchar2(20)"
or
"alter table XXX modify NEW_COL varchar2(20)".

Unfortunatly we have now a requirement which statements "alter table XXX drop NEW_COL varchar2(20)".

My trigger works fine - you see no problem directly after statement execution but the table is then in an invalid status.

The connection will be destroyed after you tried to see the data of this table.

Also the export (creating a dump) will not work.

The problem I see is that I the database will do a "modify" on a column which has internal the status "dropped".

How I can get the information what kind of alter table statement will be executed?

Or is there any chance to select only columns from USER_TAB_COLUMNS without the "dropped" flag?

create or replace trigger TRIGGER
after alter
on SCHEMA
declare
vCharSet NLS_DATABASE_PARAMETERS.VALUE%TYPE;
begin
-- Select all columns of a table

select COLUMN_NAME, DATA_TYPE, DATA_LENGTH
from USER_TAB_COLUMNS
where TABLE_NAME = vTABLE_NAME; ...

-- Loop for all columns from our select
...
vSTATEMENT := 'alter table ' || vTABLE_NAME || ' modify ' || VOBJECTREC.COLUMN_NAME || ' ' || VOBJECTREC.DATA_TYPE || '(' || vNEW_DATA_LENGTH || ')';

--For example:

-- alter table XXX modify NEW_COL varchar2(20)

execute immediate vSTATEMENT;

exception
...
end;
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