SQL>
SQL>
SQL> conn logg@test123
Enter password:
Connected.
SQL>
SQL>
SQL> CREATE OR REPLACE TRIGGER tri_ddl_alter
  2     BEFORE  ALTER  ON database ---on schema
  3  DECLARE
  4     oper   ddl_attemp_log.operation%TYPE;
  5  BEGIN
  6     SELECT ora_sysevent
  7       INTO oper
  8       FROM DUAL;
  9
 10  IF oper = 'ALTER'
 11     THEN
 12        raise_application_error   (-20997,
 13                       'ALTER In Production DB Has Been Restricted contract w
ith DBA'
 14                      );
 15
 16     END IF;
 17  END tri_ddl_alter;
 18
 19
 20  /

Trigger created.

SQL>
SQL>
SQL> create table t_1 (id number);

Table created.

SQL> ALTER TABLE t_1
  2  ADD name varchar2(20) ;
ALTER TABLE t_1
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-20997: ALTER In Production DB Has Been Restricted contract with DBA
ORA-06512: at line 10


SQL>
SQL> ALTER TRIGGER LOGG.TRI_DDL_ALTER disable;

Trigger altered.

SQL>
SQL> ALTER TRIGGER LOGG.TRI_DDL_ALTER enable;

Trigger altered.

SQL>
SQL> ALTER TRIGGER LOGG.TRI_DDL_ALTER disable;

Trigger altered.

SQL>
SQL>