ALTER TABLE my_table ADD CONSTRAINT my_table_ux1 UNIQUE (col1) DEFERRABLE INITIALLY DEFERRED NOVALIDATE;

SQL> create table t (val int);

Table created.

SQL> insert into t select 0 from dual connect by level<=3;

3 rows created.

SQL> commit;

Commit complete.

SQL> select * from t;
       VAL
----------
         0
         0
         0

3 rows selected.

SQL> select default_tablespace from user_users;
DEFAULT_TABLESPACE
------------------------------
TS_D01

1 row selected.

SQL> alter table t add constraint t_unq unique(val)
  2  DEFERRABLE INITIALLY DEFERRED NOVALIDATE
  3  using index (create index t_unq on t(val) tablespace ts_i01)
  4  /
using index (create index t_unq on t(val) tablespace ts_i01)
*
ERROR at line 3:
ORA-01735: invalid ALTER TABLE option

SQL> alter table t add constraint t_unq unique(val)
  2  DEFERRABLE INITIALLY DEFERRED -- NOVALIDATE
  3  using index (create index t_unq on t(val) tablespace ts_i01)
  4  /
alter table t add constraint t_unq unique(val)
                             *
ERROR at line 1:
ORA-02299: cannot validate (MICHEL.T_UNQ) - duplicate keys found

SQL> alter table t add constraint t_unq unique(val)
  2  DEFERRABLE INITIALLY DEFERRED disable -- NOVALIDATE
  3  using index (create index t_unq on t(val) tablespace ts_i01)
  4  /
using index (create index t_unq on t(val) tablespace ts_i01)
*
ERROR at line 3:
ORA-01735: invalid ALTER TABLE option

SQL> alter table t add constraint t_unq unique(val)
  2  DEFERRABLE INITIALLY DEFERRED
  3  using index (create index t_unq on t(val) tablespace users)
  4  NOVALIDATE
  5  /

Table altered.

SQL>

SQL> alter table t add constraint t_unq unique(val)
  2  DEFERRABLE INITIALLY DEFERRED
  3  using index (create index t_unq on t(val) tablespace users)
  4  DISABLE
  5  /

Table altered.

SQL>

[ [ [ NOT ] DEFERRABLE ]
  [ INITIALLY { IMMEDIATE | DEFERRED } ]
| [ INITIALLY { IMMEDIATE | DEFERRED } ]
  [ [ NOT ] DEFERRABLE ]
]
[ RELY | NORELY ]
[ using_index_clause ]
[ ENABLE | DISABLE ]
[ VALIDATE | NOVALIDATE ]
[ exceptions_clause ]