SQL Query where week starts first day of year.

[jmodic]

Since you don't want to answer to the very valid tamil's question about your NLS_TERRITORY setting, I'll assume you are in one of those territories where week starts on MONDAY. (If according to your NLS settings your week starts on SUNDAY, you'll have to modify the following function accordingly):

CREATE OR REPLACE FUNCTION my_non_iso_week (p_date DATE)
  RETURN INTEGER
IS
  l_first_day CHAR(1);
  l_result NUMBER(2);
BEGIN
  l_first_day := TO_CHAR(TRUNC(p_date, 'YYYY'), 'D');
  IF TO_CHAR(p_date, 'D') >= l_first_day THEN
    l_result := TO_NUMBER(TO_CHAR(p_date, 'WW'));
  ELSE
    l_result := TO_NUMBER(TO_CHAR(p_date, 'WW'))+1;
  END IF;
  RETURN l_result;
END;