Count the occurrences of how many events user hasn't responded - mysql

Question

Taking into account the tables provided below, I want to be able to count the occurrences of how many Events a User still hasn't provided availability yet.
Table users
| name | id |
|---------|----|
| John | 1 |
| Francis | 2 |
| Peter | 3 |
| Mike | 4 |
Table events
| id | name |
|----|---------|
| 1 | Event 1 |
| 2 | Event 2 |
Table availability
| answer | event_id | user_id |
|--------|----------|---------|
| yes | 1 | 1 |
| yes | 2 | 1 |
| no | 1 | 2 |
| maybe | 2 | 4 |
The expected answer would then be:
Expected answer:
| user_id | count |
|---------|-------|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 1 |
I have been able to do a query for how many events each member has responded, but looking for how many hasn't responded.
DBFiddle: https://www.db-fiddle.com/f/mwv4F1wYZ9UxB56L9mMjFQ/1
SQL:
create table events (
id int auto_increment primary key,
name varchar(100) null
);
create table users (
name varchar(100) null,
id int auto_increment primary key
);
create table availability (
answer text null,
event_id int null,
user_id int not null,
constraint availability_events_id_fk
foreign key (event_id) references events (id),
constraint availability_users_id_fk
foreign key (user_id) references users (id)
);
INSERT INTO events (id, name) VALUES (1, 'Event 1');
INSERT INTO events (id, name) VALUES (2, 'Event 2');
INSERT INTO users (name, id) VALUES ('John', 1);
INSERT INTO users (name, id) VALUES ('Francis', 2);
INSERT INTO users (name, id) VALUES ('Peter', 3);
INSERT INTO users (name, id) VALUES ('Mike', 4);
INSERT INTO availability (answer, event_id, user_id) VALUES ('yes', 1, 1);
INSERT INTO availability (answer, event_id, user_id) VALUES ('yes', 2, 1);
INSERT INTO availability (answer, event_id, user_id) VALUES ('no', 1, 2);
INSERT INTO availability (answer, event_id, user_id) VALUES ('maybe', 2, 4);

Answer 1

You can cross join tables users and events to generate all possible combinations, and then left join table availability. Then, aggregation and a conditional sum() give you the expected result.
select
u.id user_id,
sum(case when a.event_id is null then 1 else 0 end) cnt
from users u
cross join events e
left join availability a
on a.event_id = e.id and a.user_id = u.id
group by u.id
order by u.id
Demo on DB Fiddle:
user_id | cnt
------: | --:
1 | 0
2 | 1
3 | 2
4 | 1

Answer 2

You can also solve this by pre-aggregating the availability table:
select u.user_id, (e.num_events - a.cnt)
from users u left join
(select a.user_id, count(*) as cnt
from availability a
group by a.user_id
) a
on u.user_id = a.user_id cross join
(select count(*) as num_events from events) e;