How to select variables which arent connected with each other? - sql

Question

The exercise is:
Show for every Film and every Kino, if the Film is shown in the Kino
or not (Output: Filmtitel, Kino, Anzahl).
If the Film is shown in the Kino print out Anzahl>0, else print out
Anzahl 0.
I am missing the select to print out all Film if they arent shown in the Kino with Anzahl 0.
My code:
SELECT Film.Titel, Vorfuehrung.Kino, 1 AS Anzahl
FROM Film
join Vorfuehrung on Film.FID = Vorfuehrung.FILM
Code to create database:
CREATE TABLE Film
(
FID int,
Titel VARCHAR(255),
Laenge int
);
CREATE TABLE Vorfuehrung
(
Film int,
Kino VARCHAR(255)
);
Create Table Kino
(
Name VARCHAR(255),
Plaetze int,
Saele int
);
INSERT INTO Film (FID, Titel, Laenge) VALUES (1, 'Die Nase', 90);
INSERT INTO Film (FID, Titel, Laenge) VALUES (2, 'Die Hand', 85);
INSERT INTO Film (FID, Titel, Laenge) VALUES (3, 'Der Arm', 120);
INSERT INTO Film (FID, Titel, Laenge) VALUES (4, 'Das Bein', 75);
INSERT INTO Vorfuehrung (Film, Kino) VALUES (1, 'Gloria');
INSERT INTO Vorfuehrung (Film, Kino) VALUES (2, 'Gloria');
INSERT INTO Vorfuehrung (Film, Kino) VALUES (3, 'Gloria');
INSERT INTO Vorfuehrung (Film, Kino) VALUES (2, 'Apollo');
INSERT INTO Vorfuehrung (Film, Kino) VALUES (4, 'Apollo');
INSERT INTO Kino (Name, Plaetze, Saele) VALUES ('Gloria', 200, 3);
INSERT INTO Kino (Name, Plaetze, Saele) VALUES ('Apollo', 300, 2);

Answer 1

First do a cross join to get all film and kino combinations. Then left join the vorfuehrung on the fid and name (kino should probably have a surrogate key (integer) as well BTW.). Then you can GROUP BY fid, name and take the count() on any column from vorfuehrung. If a film wasn't shown in a kino, the column from vorfuehrung is NULL and therefore the row isn't counted.
SELECT f.titel,
k.name,
count(v.film) anzahl
FROM film f
CROSS JOIN kino k
LEFT JOIN vorfuehrung v
ON v.film = f.fid
AND v.kino = k.name
GROUP BY f.titel,
k.name;