declare   
    v_json clob := '{"hello":"foo"}';   
    v_hello varchar2(30);   
begin   
    select   
        value into v_hello   
    from   
        json_table(   
                    (select v_json from dual), '$'   
                    columns (value PATH '$.hello')   
);   
    dbms_output.put_line('hello: ' || v_hello);   
end;