ORACLE - How to make hierarchical query

In this example you can see hierarchical query with start with and connect by section.

• start with - is initial row (data) for question (..here key to top item).
• connect by - tells, how the new data are connected to previous row.

Here is example from BOM table:

select substr(lpad(' ', level) || level, 1, 10) as level_,
a.tl_nr, a.tl_unt_nr, a.tl_unt_fam, a.tl_unt_atn, 
a.mng_pos_re_mz as quantity, a.mng_pos_me as unit
from ertesr a
start with 
a.tl_nr = '442-97345-622-1' and
a.tl_fam = '0' and 
a.tl_atn = '02'
connect by prior a.tl_unt_nr = a.tl_nr
and prior a.tl_unt_fam = a.tl_fam
and prior a.tl_unt_atn = a.tl_atn
order by rownum

Output:

LEVEL_     TL_NR                TL_UNT_NR            TL_UNT TL_UNT   QUANTITY UN
---------- -------------------- -------------------- ------ ------ ---------- --
 1         442-97345-622-1      S-312-221-1001       0      0      ,025       KG
 1         442-97345-622-1      442-90780-566-1      0      0               1 KS
  2        442-90780-566-1      S-137-114-1060       0      0      ,6         KG
 1         442-97345-622-1      S-246-931-1005       0      0      ,019       KG
 1         442-97345-622-1      S-821-303-0144       0      0               1 KS
 1         442-97345-622-1      442-05011-145-1      0      0               2 KS
  2        442-05011-145-1      S-331-123-2058       0      0               1 KS

7 rows selected.