SQL query to check if a year is a leap year

 select &year,
       decode( mod(&year, 4), 0,
          decode( mod(&year, 400), 0, 'Leap year',
             decode( mod(&year, 100), 0, 'Not a Leap year', 'Leap Year')
          ), 'Not a Leap Year'
       ) as leap_year_indicator
from   dual;