with src as(
select 'rtyew' str from dual
union all
select 'trwye' from dual
union all
select 'trwye' from dual
union all
select 'rtgbfdsa' from dual
union all
select 'tgrbafsd' from dual
),
srcrn as(
select str, rownum rn from src
),
rec(st, c,rn,k) as(
select str, substr(str,1,1), rn, 1 from srcrn
union all
select st, substr(st,k+1,1), rn, k+1 from rec
where k<length(st)
),
res1 as (
select * from rec order by rn,c
),
res2 as(
select st,c,rn, rownum rn1 from res1
),
res as(
select distinct st,rn, substr(sys_connect_by_path(c,','),2) str from res2
where connect_by_isleaf = 1
connect by prior rn1=rn1-1 and prior rn=rn
),

maxs as(
select rn, max(length(str)) mx from res
group by rn
),
chars as(
select rs.st,rs.rn, rs.str from res rs
inner join maxs mxs on mxs.rn = rs.rn and length(str)=mxs.mx
),

preres as(
select str, min(rn) rn from chars
group by str)

select s.str from srcrn s
inner join preres p on p.rn = s.rn;