oracle日期时间型timestamp

1、获取系统时间的语句(ssxff6获取小数点后面六位)
select sysdate,systimestamp,to_char(systimestamp, \'yyyymmdd hh24:mi:ssxff6\'),
to_char(systimestamp, \'yyyymmdd hh24:mi:ss.ff6\') from dual;

2、字符型转成timestamp
select to_timestamp(\'2011-09-14 12:52:42.123456789\', \'syyyy-mm-dd hh24:mi:ss.ff\') from dual;

3、timestamp转成date型
select cast(to_timestamp(\'2011-09-14 12:52:42.123456789\', \'syyyy-mm-dd hh24:mi:ss.ff\') as date) timestamp_to_date from dual;

4、date型转成timestamp
select cast(sysdate as timestamp) date_to_timestamp from dual;

5、两date的日期相减得出的是天数，而两timestamp的日期相减得出的是完整的年月日时分秒小数秒 select sysdate-sysdate,systimestamp-systimestamp from dual;
select extract(day from inter) * 24 * 60 * 60 + extract(hour from inter) * 60 * 60 + extract(minute from inter) * 60 + extract(second from inter) "seconds" from ( select to_timestamp(\'2011-09-14 12:34:23.281000000\', \'yyyy-mm-dd hh24:mi:ss.ff\') - to_timestamp(\'2011-09-14 12:34:22.984000000\', \'yyyy-mm-dd hh24:mi:ss.ff\') inter from dual );
select extract(second from to_timestamp(\'2011-09-14 12:34:23.281000000\', \'yyyy-mm-dd hh24:mi:ss.ff\'))- extract(second from to_timestamp(\'2011-09-14 12:34:22.984000000\', \'yyyy-mm-dd hh24:mi:ss.ff\')) from dual;
注：所以，timestamp要算出两日期间隔了多少秒，要用函数转换一下。 to_char函数支持date和timestamp,但是trunc却不支持TIMESTAMP数据类型。