Oracle 18c

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create table temp_table (id number, name varchar2(30), password varchar2(30), pwd_change_date timestamp);
create trigger trig_pwd_date
before insert or update on temp_table
for each row
when (old.password is null and new.password is not null or new.password != old.password)
begin
  :new.pwd_change_date := systimestamp;
end;
/
insert into temp_table (id, name) values ('1', 'First');
1 rows affected

insert into temp_table (id, name, password) values ('2', 'Second', '12345678');
1 rows affected

select * from temp_table;


ID
NAME
PASSWORD
PWD_CHANGE_DATE


1
First
null
null

2
Second
12345678
21-SEP-20 18.25.33.158955


update temp_table set password = 'passw0rd' where id = 1;
1 rows affected

update temp_table set password = '87654321' where id = 2;
1 rows affected

select * from temp_table;


ID
NAME
PASSWORD
PWD_CHANGE_DATE


1
First
passw0rd
21-SEP-20 18.25.33.170246

2
Second
87654321
21-SEP-20 18.25.33.172119

ID	NAME	PASSWORD	PWD_CHANGE_DATE
1	First	passw0rd	21-SEP-20 18.25.33.170246
2	Second	87654321	21-SEP-20 18.25.33.172119