CREATE OR REPLACE FUNCTION is_dates (parmin VARCHAR2)
 RETURN NUMBER  IS
val DATE;
 BEGIN
 val := TO_DATE (NVL (parmin,'a'),'yyyy-MM-dd');
RETURN 1;
 EXCEPTION
WHEN OTHERS
THEN
 RETURN 0;

使用：
select  is_dates(to_char(sysdate,'yyyy-MM-dd'))  from dual