Use the count result from another query in where condition - sql

Question

I wonder how to combine two of my queries.
I have these 3 tables:
movies
movie_id PK
room_id FK
rooms
room_id PK
seats INTEGER
tickets
ticket_id PK
movie_id FK
In this simplified example, a movie only plays in a room and many tickets are sold for each movie.
I want to query which movies still have seats available.
For that I need to check
(room.seats - all tickets sold for that movie) > 0
If I do this, I get the total of tickets for each movie
SELECT movie_id, COUNT(*)
FROM tickets
GROUP BY movie_id;
And I would like to use that results in this query are condition
SELECT movie_id
FROM movies
JOIN rooms ON movies.room_id = rooms.room_id
WHERE (rooms.seats - [THE COUNT OF THE OTHER QUERY]) > 0
Does anyone if it is possible to achieve that?
Thank you in advance
I don't know how to combine two queries, it would be nice to understand how to achieve it

Answer 1

Lets assume, if data looks something like this
select
a.movie_id,
a.seats as "TOTAL_SEATS",
count(1) as "SEATS_SOLD",
a.seats - count(1) as "AVAILABLE_SEATS",
CASE when a.seats - count(1) > 0 then 'Y' else 'N' End as "SEATS_AVAILABLE"
from
(
select
m.id as movie_id,
r.seats,
t.id
from
movie m,
rooms r,
tickets t
where
m.room_id = r.id
and m.id = t.movie_id
) a
group by
a.movie_id,
a.seats
order by
movie_id asc;
Output of the Query:
If you want movie_id's specifically, for those seats that are available, then query will be as below:
select
b.movie_id
from
(
select
a.movie_id,
a.seats as "TOTAL_SEATS",
count(1) as "SEATS_SOLD",
a.seats - count(1) as "AVAILABLE_SEATS",
CASE when a.seats - count(1) > 0 then 'Y' else 'N' End as "SEATS_AVAILABLE"
from
(
select
m.id as movie_id,
r.seats,
t.id
from
movie m,
rooms r,
tickets t
where
m.room_id = r.id
and m.id = t.movie_id
) a
group by
a.movie_id,
a.seats
) b
where
b.SEATS_AVAILABLE = 'Y';
Output of the query will be:
Queries were tested on Oracle database with the above mentioned data.

Answer 2

SELECT movie_id
FROM movies
JOIN rooms ON movies.room_id = rooms.room_id
LEFT JOIN (SELECT movie_id, COUNT(*) AS C_M
FROM tickets
GROUP BY movie_id) t
ON movies.movie_id = t.movie_id and (rooms.seats - t.C_M) > 0
or : use a quantifier ALL,ANY
SELECT movie_id
FROM movies
JOIN rooms ON movies.room_id = rooms.room_id
WHERE (rooms.seats -
ANY (SELECT COUNT(*) OVER(PARTITION BY movie_id)
FROM tickets
WHERE tickets.movie_id =movies.movie_id)) > 0