with employee as ( select '2016001' id from dual union all select '2016002' id from dual union all select '2017003' id from dual union all select '2017004' id from dual union all select '2018005' id from dual union all select '2018006' id from dual ) select substr(id,1,4) yyyy from employee group by substr(id,1,4) 위 쿼리에서 substr(id,1,4) 두 번씩이나 사용해야 됩니다. 한 번만 사용하고 싶습니다. 더 좋은 방법이 있을까요?^^