I have some indexes that starts with SYS I am not able to see them in user_indexes but SQL developer explorer shows them. Any idea?
Most probably automatically generated names.
eg
SQL> create table t ( x int primary key );
Table created.
SQL>
SQL> select index_name
2 from user_indexes
3 where table_name = 'T';
INDEX_NAME
------------------------------
SYS_C0017793
An index is needed to enforce the primary key, so we automatically created one.