how to get time in millisecond from date field of oracle for the date 01-01-9999

问题

I want to get milliseconds from date field of oracle for date "01-01-9999".

I have created below block to achieve the same.

set serveroutput on;
declare
    base_point constant timestamp := to_timestamp_tz('01-JAN-1970 00:00:00.000+00:00', 'DD-Mon-RR HH24:MI:SS.FFTZH:TZM') AT TIME ZONE 'UTC';
    now timestamp := to_timestamp_tz('01-01-2099 00:00:00.000+00:00', 'DD-MM-RR HH24:MI:SS.FFTZH:TZM') AT TIME ZONE 'UTC';
    -- now constant timestamp := systimestamp AT TIME ZONE 'UTC' ;
    n number;
begin

  select to_timestamp_tz(to_char(todate,'DD-MM-YY HH24:MI:SS')||'.000+00:00','DD-MM-YY HH24:MI:SS.FFTZH:TZM')
  into now
   from t_table where ACCOUNTID = 'ACC001124211';

 DBMS_OUTPUT.put_line(' now :'||now);

 n := (
                  ((extract(day    from (now-base_point)))*86400)
                + ((extract(hour   from (now-base_point)))*3600)
                + ((extract(minute from (now-base_point)))*60)
                + ((extract(second from (now-base_point))))
           ) * 1000;

           DBMS_OUTPUT.put_line(' n :'||n);
end;
/

but using above block I am getting value as 4070908800000, which is equal to date 1/1/2099 but actual date in my table is 01-01-9999

Can you please help us to get exact millisecond using date field

回答1:

No need of PL/SQL, you could do it in plain SQL.

To convert a date to milliseconds since 01-JAN-1970:

SQL> SELECT to_number(DATE '9999-01-01'
  2         - to_date('01-JAN-1970','DD-MON-YYYY')) * (24 * 60 * 60 * 1000) milliseconds
  3  FROM dual;

      MILLISECONDS
------------------
   253370764800000

SQL>

回答2:

The reason why you are getting wrong value is this statement.

select to_timestamp_tz(to_char(todate,'DD-MM-YY HH24:MI:SS')||'.000+00:00','DD-MM-YY HH24:MI:SS.FFTZH:TZM')

Since your format element for year is YY, to_char conversion will have only 2 digits for year.

select to_char(date'9999-01-01','DD-MM-YY HH24:MI:SS')||'.000+00:00'    char_date
from dual

char_date
------------
01-01-99 00:00:00.000+00:00

When you convert this to timestamp using YY as format element, the year returned always has the same first 2 digits as the current year, which is why you get 2099 as year.

select to_char(to_timestamp_tz(to_char(date'9999-01-01','DD-MM-YY HH24:MI:SS')||'.000+00:00','DD-MM-YY HH24:MI:SS.FFTZH:TZM'),'yyyy') char_date
from dual;

char_date
------------
2099

Moral of the story:

Oracle recommends that you use the 4-digit year element (YYYY) instead of the shorter year elements for these reasons:

The 4-digit year element eliminates ambiguity.
The shorter year elements may affect query optimization because the year is not known at query compile time and can only be determined at run time.

回答3:

I've posted here some methods to convert timestamp to nanoseconds and nanoseconds to timestamp. These methods are not affected by time zones and have a nanosecond precision.

You just need to adjust it to get milliseconds instead of nanoseconds. You need to convert date to timestamp using "CAST(DATE_HERE AS TIMESTAMP)".

SELECT (EXTRACT(DAY FROM (
    CAST(SYSDATE AS TIMESTAMP) --Replace line with desired timestamp --Maximum value: TIMESTAMP '3871-04-29 10:39:59.999999999 UTC'
- TIMESTAMP '1970-01-01 00:00:00 UTC') * 24 * 60) * 60 + EXTRACT(SECOND FROM
    CAST(SYSDATE AS TIMESTAMP) --Replace line with desired timestamp
)) *  1000 AS MILLIS FROM DUAL;

MILLIS
1598447857000

来源：https://stackoverflow.com/questions/36323694/how-to-get-time-in-millisecond-from-date-field-of-oracle-for-the-date-01-01-9999

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