SELECT 1 + TRUNC (birthday_dt) - TRUNC (birthday_dt, 'IW') day_of_week 
, birthday_dt  
  + CASE 1 + TRUNC (birthday_dt) - TRUNC (birthday_dt, 'IW') 
      WHEN 6 THEN 2  
      WHEN 7 THEN 1 
      ELSE 0  
    END corrected_dt 
, to_char( 
  birthday_dt  
  + CASE 1 + TRUNC (birthday_dt) - TRUNC (birthday_dt, 'IW') 
      WHEN 6 THEN 2  
      WHEN 7 THEN 1 
      ELSE 0  
    END 
  , 'fmDay') corrected_day 
from  
( 
select to_date('19/10/2015','DD/MM/YYYY') birthday_dt from dual --monday 
union all 
select to_date('20/10/2015','DD/MM/YYYY') birthday_dt from dual 
union all 
select to_date('21/10/2015','DD/MM/YYYY') birthday_dt from dual 
union all 
select to_date('22/10/2015','DD/MM/YYYY') birthday_dt from dual 
union all 
select to_date('23/10/2015','DD/MM/YYYY') birthday_dt from dual 
union all 
select to_date('24/10/2015','DD/MM/YYYY') birthday_dt from dual 
union all 
select to_date('25/10/2015','DD/MM/YYYY') birthday_dt from dual --sunday 
)