oracle日期函数2！

1.日期时间间隔操作
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当前时间减去7分钟的时间
select sysdate,sysdate - interval '7' MINUTE from dual
当前时间减去7小时的时间
select sysdate - interval '7' hour from dual
当前时间减去7天的时间
select sysdate - interval '7' day from dual
当前时间减去7月的时间
select sysdate,sysdate - interval '7' month from dual
当前时间减去7年的时间
select sysdate,sysdate - interval '7' year from dual
时间间隔乘以一个数字
select sysdate,sysdate - 8 *interval '2' hour from dual
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2.日期到字符操作
select sysdate,to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual
select sysdate,to_char(sysdate,'yyyy-mm-dd hh:mi:ss') from dual
select sysdate,to_char(sysdate,'yyyy-ddd hh:mi:ss') from dual
select sysdate,to_char(sysdate,'yyyy-mm iw-d hh:mi:ss') from dual
 参考oracle的相关关文档(ORACLE901DOC/SERVER.901/A90125/SQL_ELEMENTS4.HTM#48515)
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3. 字符到日期操作
select to_date('2003-10-17 21:15:37','yyyy-mm-dd hh24:mi:ss') from dual
具体用法和上面的to_char差不多。
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4. trunk/ ROUND函数的使用
select trunc(sysdate ,'YEAR') from dual
select trunc(sysdate ) from dual
select to_char(trunc(sysdate ,'YYYY'),'YYYY') from dual
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5.oracle有毫秒级的数据类型
--返回当前时间年月日小时分秒毫秒
select to_char(current_timestamp(5),'DD-MON-YYYY HH24:MI:SSxFF') from dual;
--返回当前时间的秒毫秒，可以指定秒后面的精度(最大=9)
select to_char(current_timestamp(9),'MI:SSxFF') from dual;
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6.计算程序运行的时间(ms)
declare
 type rc is ref cursor;
 l_rc rc;
 l_dummy all_objects.object_name%type;
 l_start number default dbms_utility.get_time;
begin
 for I in 1 .. 1000
 loop
 open l_rc for
 'select object_name from all_objects '||

'where object_id = ' || i;
 fetch l_rc into l_dummy;
 close l_rc;
 end loop;
 dbms_output.put_line
 ( round( (dbms_utility.get_time-l_start)/100, 2 ) ||
 ' seconds...' );
end;