Oracle 18c

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select * from V$VERSION;


BANNER
BANNER_FULL
BANNER_LEGACY
CON_ID


Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
0


create table testt (id number, valst varchar2(255), valend varchar2(255), nextid number)
insert into testt (id, valst, valend, nextid)
select    1,   'MOS'  ,   'SAN'  ,    2 from dual union all
select    2,   'SAN'  ,   'MOS'  , null from dual union all
select    3,   'MOS'  ,   'EKB'  ,    4 from dual union all
select    4,   'EKB'  ,   'RYA'  ,    5 from dual union all
select    5,   'RYA'  ,   'SAN'  ,    6 from dual union all
select    6,   'SAN'  ,   'MOS'  , null from dual union all
select    7,   'MOS'  ,   'KRA'  ,    8 from dual union all
select    8,   'KRA'  ,   'VOR'  ,    9 from dual union all
select    9,   'VOR'  ,   'MOS'  , null from dual
9 rows affected

select 
    valst, level numoftrips, sys_connect_by_path (valst, ' >> ') path
from testt t
where connect_by_isleaf = 1
start with nextid is null 
connect by nextid = prior id


VALST
NUMOFTRIPS
PATH


MOS
2
 >> SAN >> MOS

MOS
4
 >> SAN >> RYA >> EKB >> MOS

MOS
3
 >> VOR >> KRA >> MOS

VALST	NUMOFTRIPS	PATH
MOS	2	>> SAN >> MOS
MOS	4	>> SAN >> RYA >> EKB >> MOS
MOS	3	>> VOR >> KRA >> MOS