Working with Functions

CREATE OR REPLACE FUNCTION is_weekend(
check_date IN DATE DEFAULT SYSDATE)
RETURN VARCHAR2 AS
BEGIN
CASE TO_CHAR(check_date,'DY')
WHEN 'SAT' THEN
RETURN 'YES';
WHEN 'SUN' THEN
RETURN 'YES';
ELSE
RETURN 'NO';
END CASE;
END;