-- Compute last Monday of a month, etc. such as Memorial Day holiday 
-- in USA - last Monday of May.
-- Input to query

-- yyyymm = 201405
-- day = MON

WITH q_base_dt AS (
 SELECT  TO_DATE(&yyyymm,'yyyymm')  ref_date  FROM  DUAL
),
q_dates AS
(SELECT
   q_base_dt.ref_date+level-1 cur_date,
   TO_CHAR(q_base_dt.ref_date+level-1,'DY') wk_day,
   ROW_NUMER() OVER(
        PARTITION BY  TO_CHAR(q_base_dt.ref_date+level-1,'DY')
        ORDER BY      q_base_dt.ref_date+level-1
      ) row_num
 FROM q_base_dt, DUAL
 CONNECT BY level <= TO_CHAR(LAST_DAY(q_base_dt.ref_date),'DD')  
),
q_max AS
(SELECT
   wk_day,
   MAX(cur_date) last_date,
   MAX(row_num)  row_num
 FROM q_dates
 GROUP BY  wk_day
)
SELECT  qdt.*
FROM q_max, q_dates qdt
WHERE q_max.row_num = qdt.row_num
AND   q_max.last_date = qdt.cur_date
AND   qdt.wk_day = UPPER('&day')
;