with t(quater, begin_ymd, end_ymd) as  (
    select 1, '0101', '0331' from dual union all
    select 2, '0401', '0630' from dual union all
    select 3, '0701', '0930' from dual union all
    select 4, '1001', '1231' from dual)
select :year year, :quater quater, :year||begin_ymd begin_ymd, :year||end_ymd end_ymd
  from t
 where quater = :quater  ;
      

SELECT y, q
     , TO_CHAR(ADD_MONTHS(TRUNC(TO_DATE(y, 'yyyy'), 'y'), q*3-3), 'yyyymmdd') s
     , TO_CHAR(ADD_MONTHS(TRUNC(TO_DATE(y, 'yyyy'), 'y'), q*3)-1, 'yyyymmdd') e
  FROM (SELECT '2016' y, '1' q FROM dual)
;

SELECT y, q
     , y || DECODE(q, 1, '0101', 2, '0401', 3, '0701', 4, '1001') s
     , y || DECODE(q, 1, '0331', 2, '0630', 3, '0930', 4, '1231') e
  FROM (SELECT '2016' y, '4' q FROM dual)
;