Code:
SQL> create table t1 (f1 number not null enable);
Table created.
SQL> create table t2 (f1 number not null disable);
Table created.
SQL> select table_name, constraint_name, constraint_type, status
2 from user_constraints;
TABLE_NAME CONSTRAINT_NAME C STATUS
------------------------------ ------------------------------ - --------
T1 SYS_C001568 C ENABLED
T2 SYS_C001569 C DISABLED
SQL> insert into t1 (f1) values (null);
insert into t1 (f1) values (null)
*
ERROR at line 1:
ORA-01400: cannot insert NULL into ("MARIST89"."T1"."F1")
SQL> insert into t2 (f1) values (null);
1 row created.
SQL> commit;
Commit complete.