Create view from 3 different tables? - mysql

Question

I'm trying to create a view in MySQL to include from 3 different tables.
CREATE TABLE ACTOR (
ACTOR_ID DECIMAL (2,0) PRIMARY KEY NOT NULL,
ACTOR_FIRST CHAR(25),
ACTOR_LAST CHAR(30),
DOB DATE
);
CREATE TABLE DIRECTOR (
DIRECTOR_ID DECIMAL(2,0) PRIMARY KEY NOT NULL,
DIRECTOR_FIRST CHAR(25),
DIRECTOR_LAST CHAR(30)
);
CREATE TABLE FILM (
FILM_ID DECIMAL(2,0) PRIMARY KEY NOT NULL,
TITLE CHAR(50),
RELEASE_DATE DATE,
DIRECTOR_ID DECIMAL(2,0),
GENRE_ID CHAR(10),
PRODUCTION_ID CHAR(3)
);
The VIEW I'm trying to create:
create view film_production as
select
title,
actor_first,
actor_last,
director_first,
director_last,
Production_id,
release_date
from film,
actor,
director
;
This gives me like 192 results. But I only have 3 actors, with 8 movies with 8 directors, and 6 production_id's. Another thing to note is 1 movie has 2 of the 3 actors in it, so I should have at least 9 movies that show not 192. I don't know what I'm doing wrong. I just cant figure this out. I'm thinking maybe a join or some kind.

Answer 1

Yes, your view should use joins.
BUT, it looks like you are missing a table, something like film_actor.
Using the missing table, and assuming you are trying to get the cast and directors of each movie it would be
SELECT
FILM.*
,ACTOR_FIRST + ' ' + ACTOR_LAST AS actor
,DIRECTOR_FIRST + ' ' + DIRECTOR_LAST AS director
FROM FILM
INNER JOIN FILM_ACTOR fa ON fa.FILM_ID = FILM.FILM_ID
INNER JOIN ACTOR ON ACTOR.ACTOR_ID = FILM_ACTOR.ACTOR_ID
INNER JOIN DIRECTOR d ON d.DIRECTOR_ID = FILM.DIRECTOR_ID
Like I mentioned, you are missing a table that would hold multiple actors and associate them to one movie: a one to many relationship.

Answer 2

Have you thought of adding referential keys between actor and film, and director and film tables?
Actor
CREATE TABLE ACTOR (
ID INT PRIMARY KEY NOT NULL,
FIRSTNAME VARCHAR(25),
LASTNAME VARCHAR(30),
DOB DATE
);
Director
CREATE TABLE DIRECTOR (
ID INT PRIMARY KEY NOT NULL,
FIRSTNAME VARCHAR(25),
LASTNAME VARCHAR(30)
);
Film with connections to actor and director
CREATE TABLE FILM (
FILM_ID INT PRIMARY KEY NOT NULL,
TITLE VARCHAR(50),
RELEASE_DATE DATE,
DIRECTOR_ID INT,
GENRE_ID INT,
PRODUCTION_ID INT,
ACTOR_ID INT,
CONSTRAINT FK_FILM_DIRECTOR_ID FOREIGN KEY (DIRECTOR_ID)
REFERENCES DIRECTOR(ID),
CONSTRAINT FK_FILM_ACTOR_ID FOREIGN KEY (ACTOR_ID)
REFERENCES ACTOR(ID)
);
View combining the 3 tables
create view film_production as
select
title,
a.firstname as actor_firstname,
a.lastname as actor_lastname,
d.firstname as director_firstname,
d.lastname as directory_lastname,
Production_id,
release_date
from film f
left join actor a on f.actor_id = a.id
left join director d on f.director_id = d.id;
Example: http://sqlfiddle.com/#!9/9fe1e
Note that I have used INT instead of DECIMAL for ID fields and VARCHAR instead of CHAR fields. This may help in allocating the right space for most general purpose uses.