PLSQL_基础系列9_时间戳Timestamp

2013-11-09 BaoXinjian

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。