1  –  CASCADE

    The CASCADE clause specifies that you want SQL to invalidate
    all objects that refer to the sequence and then delete the
    sequence definition. If you delete a sequence referenced by a
    stored routine or trigger with a routine or language-semantic
    dependency, SQL also marks the affected stored routine or trigger
    as invalid.

2  –  IF_EXISTS

    Prevents SQL command language from displaying error messages if
    the referenced object does not exist in the database.

3  –  RESTRICT

    The RESTRICT clause prevents the removal of a sequence definition
    (the DROP SEQUENCE statement fails) when the sequence is
    referenced by any other object within the Oracle Rdb database.

    The RESTRICT clause is the default.

4  –  sequence-name

    An existing sequence name in the database. To specify lowercase
    characters or characters not in the SQL repertoire, enclose the
    sequence name in single quotation marks (').