create before insert trigger to add sysdate + 30 minutes in sql - sql

Question

i have table with timestamp column
i want to add on each insert
to add the current timestamp + 30 minutes
how to achieve that
im using oracle 11g;

Answer 1

As you have a timestamp column it's probably better to use systimestamp instead of sysdate, and add an interval rather than a fraction of a day - which would lose the fractional second precision (and time zone, if your column actually stores that too).
You would either just have a date (if you use sysdate + 30/1440) or implicitly convert to a date (if you use systimestamp + 30/1440); and either way will you'll end up with a date that is then implicitly or explicitly converted to a timestamp as it's stored in your column.
As a simple example of using an interval:
create table t42 (col1 number, col2 timestamp);
create trigger tr42
before insert on t42
for each row
begin
:new.col2 := systimestamp + interval '30' minute;
end;
/
select systimestamp from dual;
SYSTIMESTAMP
---------------------------------
2019-02-13 07:17:11.971542000 GMT
insert into t42 (col1) values (42);
select col1, col2 from t42;
COL1 COL2
---------- -----------------------------
42 2019-02-13 07:47:12.253603000
You could also use a default value for the column instead of a trigger:
create table t42 (
col1 number,
col2 timestamp default systimestamp + interval '30' minute
);
select systimestamp from dual;
SYSTIMESTAMP
---------------------------------
2019-02-13 07:17:12.962268000 GMT
insert into t42 (col1) values (42);
select col1, col2 from t42;
COL1 COL2
---------- -----------------------------
42 2019-02-13 07:47:13.028670000
although that does allow the person doing the insert to provide their own value:
insert into t42 (col1, col2) values (43, timestamp '2000-01-01 00:00:00.0');
select col1, col2 from t42;
COL1 COL2
---------- -----------------------------
42 2019-02-13 07:47:13.028670000
43 2000-01-01 00:00:00.000000000
The trigger would override any user-supplied value (though it could also be modified not to.)
You could also use current_timestamp instead of systimestamp - they do slightly different things.

Answer 2

you can create a trigger as shown below. this will insert current timestamp+30 minutes each time you insert a row to the table.
create or replace trigger before_insert
before insert
on table_name for each row
declare
v_time date;
begin
select sysdate+30/1440 into v_time from dual;
:new.cur_time :=v_time;
end;
/