There are 15 tables,

  1. actor
--
-- Name: actor; Type: TABLE; Schema: public; Owner: postgres
--

CREATE TABLE public.actor (
    actor_id integer DEFAULT nextval('public.actor_actor_id_seq'::regclass) NOT NULL,
    first_name character varying(45) NOT NULL,
    last_name character varying(45) NOT NULL,
    last_update timestamp without time zone DEFAULT now() NOT NULL
);

This SQL script creates a table named "actor" in the "public" schema of a PostgreSQL database. The table has four columns:

Overall, this table is used to store information about actors in a movie database.

In PostgreSQL, the "character varying" data type and the "varchar" data type are interchangeable and have the same meaning. Both data types allow you to specify a variable-length string with a maximum length of 45 characters in this case.

The difference between "character varying" and "char" data types is that "character varying" is a variable-length string data type, while "char" is a fixed-length string data type. When you define a "char" column with a length of 45, it will always use 45 bytes of storage, even if the actual value stored in the column is shorter. In contrast, a "character varying" column with a length of 45 will only use the necessary amount of storage to store the actual value.

  1. film
CREATE TABLE public.film (
    film_id integer DEFAULT nextval('public.film_film_id_seq'::regclass) NOT NULL,
    title character varying(255) NOT NULL,
    description text,
    release_year public.year,
    language_id smallint NOT NULL,
    original_language_id smallint,
    rental_duration smallint DEFAULT 3 NOT NULL,
    rental_rate numeric(4,2) DEFAULT 4.99 NOT NULL,
    length smallint,
    replacement_cost numeric(5,2) DEFAULT 19.99 NOT NULL,
    rating public.mpaa_rating DEFAULT 'G'::public.mpaa_rating,
    last_update timestamp without time zone DEFAULT now() NOT NULL,
    special_features text[],
    fulltext tsvector NOT NULL,
    revenue_projection numeric(5,2) GENERATED ALWAYS AS (((rental_duration)::numeric * rental_rate)) STORED
);

This SQL statement creates a table named film in the public schema. The table has the following columns:

Overall, this film table stores information about movies in a rental store, including their title, description, rental duration, rental rate, and more. The generated column revenue_projection is useful for generating reports or analyzing the profitability of each movie.

  1. film_actor
--
-- Name: film_actor; Type: TABLE; Schema: public; Owner: postgres
--

CREATE TABLE public.film_actor (
    actor_id smallint NOT NULL,
    film_id smallint NOT NULL,
    last_update timestamp without time zone DEFAULT now() NOT NULL
);

The film_actor table is a junction table used to establish a many-to-many relationship between the film table and the actor table.

The film_actor table has two columns: actor_id and film_id, which are both foreign keys that reference the actor_id and film_id columns in the actor and film tables, respectively. This means that each row in the film_actor table represents a relationship between an actor and a film, indicating that the actor appears in the specified film.

The last_update column in the film_actor table is a timestamp that records when the relationship between the actor and the film was last updated. This can be useful for auditing purposes or for tracking changes to the relationships over time.

Overall, the film_actor table is an important part of the database schema for a movie rental application, as it allows the application to efficiently query and manage relationships between actors and films.

So, many-to-many need not be defined somehere, it was impiled in the CREATE TABLE definition? Yes, the fact that a many-to-many relationship exists between the actor and film tables is implied by the existence of the film_actor table.

A many-to-many relationship between two tables is typically represented by a third table (such as the film_actor table in this case) that contains foreign keys that reference the primary keys of the two original tables. This junction table is used to establish the relationship between the two original tables.

By creating the film_actor table with foreign keys that reference the actor and film tables, we are implying that a many-to-many relationship exists between these two tables. Therefore, we don't explicitly need to define the relationship as a many-to-many relationship in the CREATE TABLE statement.

CREATE TABLE public.film_actor ( actor_id smallint NOT NULL, film_id smallint NOT NULL, last_update timestamp without time zone DEFAULT now() NOT NULL );

alexlai@munetaka.me So, inside film_actor's column name actor_id is a column name in actor's table makes it to be a foreign key. Yes, that's correct. The actor_id column in the film_actor table is a foreign key that references the actor_id column in the actor table.

A foreign key is a column or a set of columns in a table that refer to the primary key or a unique constraint of another table. The purpose of a foreign key is to enforce referential integrity, which means that the values in the foreign key column(s) must exist in the referenced table.

In the case of the film_actor table, the actor_id column references the actor_id column in the actor table, which means that every value in the actor_id column of the film_actor table must exist in the actor_id column of the actor table. This ensures that only valid actors can be associated with films in the film_actor table.