How can I add the current date in ORACLE SQL column? - sql

Question

How can I add the "now" date in a column? I want to achieve the following scenario: if I insert a row today the date column will have the value 25/10/2021 and if tomorrow I'll execute a SELECT statement, I want to see that column updated with the value 26/10/2021 and so on. Is there a way to keep the column updated without me doing anything manually? Thanks.
Later edit: I want to use that column for a PERIOD in a temporal table. Example: PERIOD FOR example_period(some_date, now_date)

Answer 1

In your request comments you have altered your request fundamentally.
One problem: You have an open date range, with a beginning date and an ending date. But when displaying this, you want to substitute the no end" with the current date. This is usually done by storing null (no value) for the date. In a query you can then use COALESCE to replace that with the current date:
SELECT
empno,
salary,
start_date AS first_day,
COALESCE(end_date, TRUNC(SYSDATE)) AS last_day
FROM salaries;
And for convenience you can make this a view:
CREATE VIEW v_salaries AS SELECT <above query>
Another problem is that you want this null to change when a newer salary information gets added.
Manually you would just
INSERT INTO salaries (empno, salary, start_date, end_date)
VALUES(50, 1200, TRUNC(SYDATE), NULL);
UPDATE salaries SET end_date = TRUNC(SYSDATE) - 1
WHERE empno = 50 AND end_date IS NULL;
If you want this update to happen automatically, there are mainly two options:
write a procedure for a new salary that does the insert and update
write a trigger to perform the update

Answer 2

That doesn't make any sense. It is as if you'd just
select empno, ename,
sysdate --> this
from employees
every time.
SELECT won't update any column value, so ... why would you store such a date in the first place, if you want to keep it synchronized with sysdate?
But, if you want Oracle to insert sysdate into that column as its default value, you'd then create column as such, e.g.
SQL> create table test
2 (id number,
3 datum date default sysdate
4 );
Table created.
SQL> alter session set nls_date_format = 'dd.mm.yyyy hh24:mi:ss';
Session altered.
SQL> insert into test (id) values (1);
1 row created.
SQL> select * from test;
ID DATUM
---------- -------------------
1 25.10.2021 14:05:02
SQL>
But, it would remain the same "forever", unless you actually update its value.

Answer 3

Add a trigger that fill a column with sysdate :
create or replace TRIGGER TRG_FILL_DATE
BEFORE INSERT ON MY_TABLE
FOR EACH ROW
WHEN (NEW.MY_DATE_COLUMN IS NULL)
BEGIN
SELECT sysdate INTO :NEW.MY_DATE_COLUMN FROM DUAL;
END;
Or as suggested use 'DEFAULT sysdate' on your column.

Answer 4

You can use a generated column:
CREATE TABLE salaries (
id NUMBER(10,0)
GENERATED ALWAYS AS IDENTITY
CONSTRAINT salaries__id__pk PRIMARY KEY,
emp_id CONSTRAINT salaries__emp_id__fk REFERENCES employees (id)
NOT NULL,
salary NUMBER(12,2)
NOT NULL,
start_date DATE
NOT NULL,
end_date DATE
NULL,
assumed_end_date DATE
GENERATED ALWAYS AS (date_or_now(end_date))
NOT NULL
);
and create the DETERMINISTIC function (in a slight abuse of how it is supposed to be used):
CREATE FUNCTION date_or_now (dt IN DATE) RETURN DATE DETERMINISTIC
IS
BEGIN
RETURN COALESCE(dt, SYSDATE);
END;
/
Then if you:
INSERT INTO salaries (emp_id, salary, start_date)
VALUES (1, 123, DATE '2021-01-01');
Then:
SELECT *
FROM salaries;
The output is:
ID
EMP_ID
SALARY
START_DATE
END_DATE
ASSUMED_END_DATE
1
1
123
2021-01-01 00:00:00
2021-10-25 13:28:08
Then if you do:
UPDATE salaries
SET END_DATE = DATE '2021-10-01'
WHERE id = 1;
INSERT INTO salaries (emp_id, salary, start_date)
VALUES (1, 234, DATE '2021-10-01');
Then:
SELECT *
FROM salaries;
The output is:
ID
EMP_ID
SALARY
START_DATE
END_DATE
ASSUMED_END_DATE
1
1
123
2021-01-01 00:00:00
2021-10-01 00:00:00
2021-10-01 00:00:00
2
1
234
2021-10-01 00:00:00
2021-10-25 13:28:08
db<>fiddle here