updating row on other table after trigger event

[gustavo morales]

Hi thanks for your time.

I have the following tables:

create table `user_keys`(
id_user int(5),
id_key int(5),
constraint pk_uk primary key(id_user, id_key),
constraint fk_uk_k foreign key(id_key) references `keys`(id),
constraint fk_uk_k foreign key(id_key) references `keys`(id));

create table `keys`(
id int(5),
`key` varchar(20),
`used`int(5),
constraint pk primary key(id));

I use these tables to keep track of which user has which key.
for an example's sake, imagine this tables have the following data:

USER_KEYS:
id_user______id_key
1____________ 1
2____________ 1
3____________ 2

`keys`:

id______key____________used
1_______CHVWX __________2
2_______ABCD2 __________1


Table user_keys stores a the user ID and key ID.
What I'd like to do is, when you delete a registry on user_keys for example, registry 1, have a trigger that updates table `keys` such as:

UPDATE `keys` SET used = used - 1 where $$here is the problem$$

I wonder if it's overly complicated trying to do this with a trigger, because it's rather easy with 2 queries such as:

DELETE from `user_keys` WHERE id_key = $variable and id_user = $variable2;
UPDATE `keys` SET used = used - 1 where id = $variable;