You cannot modify aliases or synonyms in Oracle and DB2. If the definition of a synonym (alias) must be changed, you can drop and re-create it using DROP SYNONYM (ALIAS) and CREATE SYNONYM (ALIAS).
The syntax to destroy an Oracle synonym is
DROP [PUBLIC] SYNONYM <synonym_name>;
You must use the PUBLIC keyword if the synonym you are going to remove was created as a public synonym. Assuming the examples from Chapter 4,
DROP PUBLIC SYNONYM SHIPMENT;
Oracle does not invalidate any objects that the dropped synonym was referring to except for materialized views.
The syntax to remove an alias in DB2 is
DROP {ALIAS | SYNONYM} <alias_name>
For example
DROP ALIAS SHIPMT
All tables, views, and triggers that reference the dropped alias become inoperative.