SQL> create table empx as select * from emp;

Table created.

SQL> select ename,deptno
   2   from empx
   3   start with job in (select 'PRESIDENT' from dual)
   4   connect by prior empno = mgr;

Execution Plan
 ----------------------------------------------------------
 
    0       SELECT STATEMENT Optimizer=CHOOSE
    1      0    CONNECT BY (WITH FILTERING)
    2      1      NESTED LOOPS
    3      2        MERGE JOIN
    4      3          SORT (JOIN)
    5      4            TABLE ACCESS (FULL) OF 'EMPX'
    6      3          SORT (JOIN)
    7      6            VIEW OF 'VW_NSO_1'
    8      7              SORT (UNIQUE)
    9      8                TABLE ACCESS (FULL) OF 'DUAL'
   10      2        TABLE ACCESS (BY USER ROWID) OF 'EMPX'
   11      1      NESTED LOOPS
   12     11        BUFFER (SORT)
   13     12          CONNECT BY PUMP
   14     11        TABLE ACCESS (FULL) OF 'EMPX'
   15      1      FILTER
   16     15        TABLE ACCESS (FULL) OF 'DUAL'

SQL> create index empx_idx1 on empx(job);

Index created.

SQL> select ename,deptno
   2   from empx
   3   start with job in (select 'PRESIDENT' from dual)
   4   connect by prior empno = mgr;

Execution Plan
 ----------------------------------------------------------
 
    0       SELECT STATEMENT Optimizer=CHOOSE
    1      0    CONNECT BY (WITH FILTERING)
    2      1      NESTED LOOPS
    3      2        NESTED LOOPS
    4      3          VIEW OF 'VW_NSO_1'
    5      4            SORT (UNIQUE)
    6      5              TABLE ACCESS (FULL) OF 'DUAL'
    7      3          INDEX (RANGE SCAN) OF 'EMPX_IDX1' (NON-UNIQUE)
    8      2        TABLE ACCESS (BY USER ROWID) OF 'EMPX'
    9      1      NESTED LOOPS
   10      9        BUFFER (SORT)
   11     10          CONNECT BY PUMP
   12      9        TABLE ACCESS (FULL) OF 'EMPX'
   13      1      FILTER
   14     13        TABLE ACCESS (FULL) OF 'DUAL'

SQL> create index empx_idx2 on empx(mgr);

Index created.

SQL> select ename,deptno
   2   from empx
   3   start with job in (select 'PRESIDENT' from dual)
   4   connect by prior empno = mgr;

Execution Plan
 ----------------------------------------------------------
 
    0       SELECT STATEMENT Optimizer=CHOOSE
    1      0    CONNECT BY (WITH FILTERING)
    2      1      NESTED LOOPS
    3      2        NESTED LOOPS
    4      3          VIEW OF 'VW_NSO_1'
    5      4            SORT (UNIQUE)
    6      5              TABLE ACCESS (FULL) OF 'DUAL'
    7      3          INDEX (RANGE SCAN) OF 'EMPX_IDX1' (NON-UNIQUE)
    8      2        TABLE ACCESS (BY USER ROWID) OF 'EMPX'
    9      1      NESTED LOOPS
   10      9        BUFFER (SORT)
   11     10          CONNECT BY PUMP
   12      9        TABLE ACCESS (BY INDEX ROWID) OF 'EMPX'
   13     12          INDEX (RANGE SCAN) OF 'EMPX_IDX2' (NON-UNIQUE)
   14      1      FILTER
   15     14        TABLE ACCESS (FULL) OF 'DUAL'