interval相关

SELECT ASCII('a') from dual;--97
SELECT CHR(10) FROM dual; --换行符
SELECT SYSTIMESTAMP FROM dual; --精确到10-6次方秒
 SELECT numtodsinterval('333', 'second') FROM dual;
 SELECT numtodsinterval('333', 'minute') FROM dual;
 SELECT numtodsinterval('333', 'day') FROM dual;
 SELECT numtoyminterval('33','year') FROM dual;
 SELECT numtoyminterval('33','MONTH') FROM dual;
 SELECT to_dsinterval('3 00:00:01') FROM dual;
 SELECT to_yminterval('3-3') FROM dual;
A extract 抽取date型  

SELECT EXTRACT (YEAR FROM SYSDATE) FROM dual;
   SELECT EXTRACT (MONTH FROM SYSDATE) FROM dual;
  SELECT EXTRACT (DAY FROM SYSDATE) FROM dual;
    SELECT EXTRACT (HOUR FROM SYSDATE) FROM dual;    --error
    SELECT EXTRACT (MINUTE FROM SYSDATE) FROM dual;   --error
   SELECT EXTRACT (SECOND FROM SYSDATE) FROM dual;    --error
 --注意： 如果真要从日期类型的字段中抽取时\分部分用to_char()函数就可以了.比如to_char(日期类型,'hh24:mi')

B、extract 抽取interval型 （同理不能抽取时分秒） 

   SELECT EXTRACT (YEAR FROM numtoyminterval('333', 'month') ) FROM dual;
   SELECT EXTRACT (MONTH FROM numtoyminterval('33','MONTH')) FROM dual;