Add and subtract operations for Oracle dates

Both date and timestamp can be added and reduced.
There are three ways to manipulate different time types for the current date Gagnin, month, day, hour, minute, and second:

1 add hours, minutes and seconds using built-in functions Numtodsinterval
2 plus a simple number to increase the day
3 use built-in function add_months to increase year and month

Cases:
Add one hours to the current date:
Sql> Select Sysdate, Sysdate+numtodsinterval (1, ' Hour ') from dual;

Sysdate Sysdate+numtodsinte
——————- ——————-
2010-10-14 21:38:19 2010-10-14 22:38:19
Add 50 minutes to the current date
Sql> Select Sysdate, Sysdate+numtodsinterval (' minute ') from dual;

Sysdate Sysdate+numtodsinte
——————- ——————-
2010-10-14 21:39:12 2010-10-14 22:29:12
Add 45 seconds to the current date
Sql> Select Sysdate, Sysdate+numtodsinterval ("second") from dual;

Sysdate Sysdate+numtodsinte
——————- ——————-
2010-10-14 21:40:06 2010-10-14 21:40:51
Add 3 days to the current date
Sql> Select Sysdate, sysdate+3 from dual;

Sysdate sysdate+3
——————- ——————-
2010-10-14 21:40:46 2010-10-17 21:40:46
Add 4 months to the current date
Sql> Select Sysdate, Add_months (sysdate,4) from dual;

Sysdate add_months (Sysdate,
——————- ——————-
2010-10-14 21:41:43 2011-02-14 21:41:43

2 year increase in current date
Sql> Select Sysdate, Add_months (sysdate,12*2) from dual;

Sysdate add_months (Sysdate,
——————- ——————-
2010-10-14 21:42:17 2012-10-14 21:42:17

The operation method of timestamp is similar to the above;
Ask for the difference of two dates:
Example: To find the difference between the 21:23:34 and the current time in 2007-5-23.
Sql> Select Sysdate-to_date (' 20070523 21:23:34′, ' yyyy-mm-dd hh24:mi:ss ') DT from
Dual;

Dt
———-
1240.01623
If the two date is directly subtracted, the result is a data type, we may want to get two date difference in the expression form:
* * * * * * * * * * * *:* *:* *
Sql> SELECT Numtoyminterval (Months_between (DT1, DT2), ' month ') Mon,
2 Numtodsinterval (dt1-(Add_months (Dt2,trunc (Months_between, DT1))
"Day") Day
3 from (SELECT sysdate DT1,
4 to_date (' 20070523 21:23:34′, ' yyyy-mm-dd hh24:mi:ss ') DT2
5 from DUAL)
6;

MON Day
—————- ———————-
+000000003-04 +000000021 00:40:15.999999999

namely: 3 years 4 months 21 days 00:40:15.99999999