ORACLE converts data between milliseconds and dates, and oracle converts data between milliseconds.

ORACLE converts data between milliseconds and dates, and oracle converts data between milliseconds.

Convert millisecond to date

SELECT TO_CHAR(1406538765000 / (1000 * 60 * 60 * 24) +      
        TO_DATE('1970-01-01 08:00:00', 'YYYY-MM-DD HH:MI:SS'), 'YYYY-MM-DD HH24:MI:SS') AS CDATE      
 FROM DUAL; 

Date conversion in milliseconds

 SELECT TO_NUMBER(TO_DATE('2014-07-28 17:12:45', 'YYYY-MM-DD HH24:MI:SS') -      
                 TO_DATE('1970-01-01 8:0:0', 'YYYY-MM-DD HH24:MI:SS')) * 24 * 60 * 60 * 1000      
  FROM DUAL; 

Obtain the current system time

select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;

Note: The time for converting millisecond to date format can be 12-hour or 24-hour.

In oracle, how does one convert the system time to milliseconds?

This problem ....
Let me give you a detailed answer, so I will not worry about any questions in this regard.

Oracle Computing Time Difference Expression

-- Obtain the number of seconds of the difference between the two time periods
Select ceil (To_date ('2017-05-02 00:00:00 ', 'yyyy-mm-dd hh24-mi-ss')-To_date ('2017-04-30 23:59:59 ', 'yyyy-mm-dd hh24-mi-ss ') * 24*60*60*1000) the number of seconds from dual;
/*
Difference in luxury seconds
----------
86401000
1 row selected
*/

-- Obtain the time difference in seconds
Select ceil (To_date ('2017-05-02 00:00:00 ', 'yyyy-mm-dd hh24-mi-ss')-To_date ('2017-04-30 23:59:59 ', 'yyyy-mm-dd hh24-mi-ss ') * 24*60*60) Time Difference from dual;
/*
Difference in seconds
----------
86401
1 row selected
*/

-- Get the minute-to-minute difference between the two time periods
Select ceil (To_date ('2017-05-02 00:00:00 ', 'yyyy-mm-dd hh24-mi-ss')-To_date ('2017-04-30 23:59:59 ', 'yyyy-mm-dd hh24-mi-ss ') * 24*60) number of minutes from dual;
/*
Minutes of difference
----------
1441
1 row selected
*/

-- Get the hours of difference between the two time periods
Select ceil (To_date ('2017-05-02 00:00:00 ', 'yyyy-mm-dd hh24-mi-ss')-To_date ('2017-04-30 23:59:59 ', 'yyyy-mm-dd hh24-mi-ss ') * 24) hours from dual;
/*
Time Difference
----------
25
1 row selected
*/

-- Get the number of days of the difference between the two time periods
Select ceil (To_date ('2017-05-02 00:00:00 ', 'yyyy-mm-dd hh24-mi-ss')-To_date ('2017-04-30 23:59:59 ', 'yyyy-mm-dd hh24-mi-ss ') days from dual;
/*
Days difference
----------
2
1 row selected
*/

----------------------------------------
Note: The number of days can be directly reduced by two days, which is more convenient.
----------------------------------------

-- Get the two-time month difference
Select (EXTRACT (year ...... remaining full text>

Conversion of oracle date data

SQL> select extract (day from (to_date ('2017-05-11 15:10:24 ', 'yyyy-mm-dd hh24: mi: ss ') -to_date ('1970-01-01 00:00:00 ', 'yyyy-mm-dd hh24: mi: ss') day (0) to second (0 )) * 24*60*60
2 + extract (hour from (to_date ('2017-05-11 15:10:24 ', 'yyyy-mm-dd hh24: mi: ss ') -to_date ('1970-01-01 00:00:00 ', 'yyyy-mm-dd hh24: mi: ss') day (0) to second (0) * 60*60
3 + extract (minute from (to_date ('2017-05-11 15:10:24 ', 'yyyy-mm-dd hh24: mi: ss ') -to_date ('1970-01-01 00:00:00 ', 'yyyy-mm-dd hh24: mi: ss') day (0) to second (0) * 60
4 + extract (second from (to_date ('2017-05-11 15:10:24 ', 'yyyy-mm-dd hh24: mi: ss ') -to_date ('1970-01-01 00:00:00 ', 'yyyy-mm-dd hh24: mi: ss') day (0) to second (0 ))
5 from dual;

EXTRACT (DAYFROM (TO_DATE ('2017-
------------------------------
1336749024
SQL> select to_date ('1970-01-01 00:00:00 ', 'yyyy-mm-dd hh24: mi: ss') + numtodsinterval (1970, 'second') from dual;

TO_DATE ('2017-01-0100:00:00 ','
------------------------------
03:10:24

SQL>
The above are mutually verified. If it is helpful, please adopt