Getting "invalid NEW or OLD specification" message when I try to run this - sql

Question

The entire question I'm trying to answer is:
Utilize the travel anywhere database to create a database trigger "hotel_kids_rule" to enforce a business rule. when inserting a hotel_reservation, if the num_kids value is more than zero, then assign the bed_type DQ to the reservation. save the trigger source as a script file.
For example, the trigger will change the bed_type for the following insert statement.
insert into hotel_reservation (reserve_no,reserve_date,arrival_date,dep_date,num_adults,num_kids,customer_id,hotel_id,bed_type,rooms)
values(hotel_reserve_sequence.nextval,sysdate,sysdate+5,sysdate+7,1,2,101,19,'DT',1);
For example, the trigger will not change the bed_type for the following insert statement.
insert into hotel_reservation (reserve_no,reserve_date,arrival_date,dep_date,num_adults,num_kids,customer_id,hotel_id,bed_type,rooms)
values(hotel_reserve_sequence.nextval,sysdate,sysdate+5,sysdate+7,2,0,102,20,'DT',1);
This is what I have so far:
create or replace trigger hotel_kids_rule
after insert or update on hotel_reservation
for each row
when (num_kids > 0)
declare
new_bed_type varchar2(20);
new_bed_type='DQ'
begin
new.bed_type=new_bed_type;
end;
Any help would be appreciated! Thanks!

Answer 1

I think you want a before trigger, so you can set the new value before it is written. Also, the way you access new is not ok: within the trigger code, you need :new.bed_type; in the when condition, you want new.num_kids.
This should work:
create or replace trigger hotel_kids_rule
before insert or update on hotel_reservation
for each row
when (new.num_kids > 0)
begin
:new.bed_type := 'DQ';
end;
/
Here is a small demo.

Answer 2

The assignment of your variable needs to be inside the actual code block. And the assignment operator is := in PL/SQL, not =. If you want the trigger to change anything you also need to create it as a BEFORE trigger:
create or replace trigger hotel_kids_rule
before insert or update on hotel_reservation
for each row
when (new.num_kids > 0)
declare
new_bed_type varchar2(20);
begin
new_bed_type := 'DQ';
:new.bed_type := new_bed_type;
end;
Note that the new record in the when condition is used without the colon : while inside the code block it needs to be referenced with the colon.
Alternatively initialize the variable when declaring it:
declare
new_bed_type varchar2(20) := 'DQ';
begin
:new.bed_type := new_bed_type;
end;
Or even simpler without any intermediate variable.
begin
:new.bed_type := 'DQ';
end;