Oracle 18c

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-- original
with rws as (
  select 'Bob' person, 'AB,CR,DE' str from dual UNION ALL 
  select 'Jane' person, 'AB' str from dual 
)
  select person,
       regexp_substr (
           str,
           '[^,]+',
           1,
           level
         ) value
  from   rws
  connect by level <= 
    length ( str ) - length ( replace ( str, ',' ) ) + 1
ORDER BY person, str;


PERSON
VALUE


Bob
AB

Bob
CR

Bob
DE

Bob
DE

Bob
CR

Jane
AB


with rws as (
  select 'Bob' person, 'AB,CR,DE' str from dual UNION ALL 
  select 'Jane' person, 'AB' str from dual 
)
  select person,
       regexp_substr (
           str,
           '[^,]+',
           1,
           level
         ) value
  from   rws
  connect by level <= 
    length ( str ) - length ( replace ( str, ',' ) ) + 1
  and prior person = person
--  and prior dbms_random.value is not null
ORDER BY person, str;
ORA-01436: CONNECT BY loop in user data

with rws as (
  select 'Bob' person, 'AB,CR,DE' str from dual UNION ALL 
  select 'Jane' person, 'AB' str from dual 
)
  select person,
       regexp_substr (
           str,
           '[^,]+',
           1,
           level
         ) value
  from   rws
  connect by level <= 
    length ( str ) - length ( replace ( str, ',' ) ) + 1
  and prior person = person
  and prior dbms_random.value is not null
ORDER BY person, str;


PERSON
VALUE


Bob
AB

Bob
CR

Bob
DE

Jane
AB


with rws as (
  select 'Bob' person, 'AB,CR,DE' str from dual UNION ALL 
  select 'Jane' person, 'AB' str from dual 
),
rcte (person, str, cnt, lvl, value) as (
  select person, str, length ( str ) - length ( replace ( str, ',' ) ), 1,
       regexp_substr (
           str,
           '[^,]+',
           1,
           1
         )
  from   rws
  union all
  select person, str, cnt, lvl + 1,
       regexp_substr (
           str,
           '[^,]+',
           1,
           lvl + 1
         )
  from   rcte
  where  lvl <= cnt
)
select person, value
from rcte
order by person, value;


PERSON
VALUE


Bob
AB

Bob
CR

Bob
DE

Jane
AB