select regexp_substr('123,456,789','+') from dual --123
select regexp_substr('123,456,789','+',1,2) from dual --456
select regexp_substr('123,456,789','+',1,3) from dual --789
select regexp_substr('123,456,789','+',2,1) from dual --23
select regexp_substr('123,456,789','+',2,2) from dual --456
select regexp_substr('123,456,789','+',2,3) from dual --789
select regexp_substr('123,456,789','+',3,3) from dual --789