with x as ( 
    select 1 as i, 'A' as j from dual union all select 1, 'A' from dual union all select 1, 'A' from dual  
    union all 
    select 2, 'D' from dual union all select 2, 'D' from dual union all select 2, 'E' from dual  
    union all  
    select 3, 'G' from dual union all select 3, 'H' from dual union all select 3, 'H' from dual 
    ) 
select x.i,  
    listagg(distinct x.j, ', ') within group (order by x.j) as X_LIST, 
    json_arrayagg(distinct x.j order by x.j) as X_JSON 
from x 
group by x.i