CSV file data into a PostgreSQL table - postgresql

Question

I am trying to create a database for movielens (http://grouplens.org/datasets/movielens/). We've got movies and ratings. Movies have multiple genres. I splitted those out into a separate table since it's a 1:many relationship. There's a many:many relationship as well, users to movies. I need to be able to query this table multiple ways.
So I created:
CREATE TABLE genre (
genre_id serial NOT NULL,
genre_name char(20) DEFAULT NULL,
PRIMARY KEY (genre_id)
)
.
INSERT INTO genre VALUES
(1,'Action'),(2,'Adventure'),(3,'Animation'),(4,'Children\s'),(5,'Comedy'),(6,'Crime'),
(7,'Documentary'),(8,'Drama'),(9,'Fantasy'),(10,'Film-Noir'),(11,'Horror'),(12,'Musical'),
(13,'Mystery'),(14,'Romance'),(15,'Sci-Fi'),(16,'Thriller'),(17,'War'),(18,'Western');
.
CREATE TABLE movie (
movie_id int NOT NULL DEFAULT '0',
movie_name char(75) DEFAULT NULL,
movie_year smallint DEFAULT NULL,
PRIMARY KEY (movie_id)
);
.
CREATE TABLE moviegenre (
movie_id int NOT NULL DEFAULT '0',
genre_id tinyint NOT NULL DEFAULT '0',
PRIMARY KEY (movie_id, genre_id)
);
I dont know how to import my movies.csv with columns movie_id, movie_name and movie_genre For example, the first row is (1;Toy Story (1995);Animation|Children's|Comedy)
If I INSERT manually, it should be look like:
INSERT INTO moviegenre VALUES (1,3),(1,4),(1,5)
Because 3 is Animation, 4 is Children and 5 is Comedy
How can I import all data set this way?

Answer 1

You should first create a table that can ingest the data from the CSV file:
CREATE TABLE movies_csv (
movie_id integer,
movie_name varchar,
movie_genre varchar
);
Note that any single quotes (Children's) should be doubled (Children''s). Once the data is in this staging table you can copy the data over to the movie table, which should have the following structure:
CREATE TABLE movie (
movie_id integer, -- A primary key has implicit NOT NULL and should not have default
movie_name varchar NOT NULL, -- Movie should have a name, varchar more flexible
movie_year integer, -- Regular integer is more efficient
PRIMARY KEY (movie_id)
);
Sanitize your other tables likewise.
Now copy the data over, extracting the unadorned name and the year from the CSV name:
INSERT INTO movie (movie_id, movie_name)
SELECT parts[1], parts[2]::integer
FROM movies_csv, regexp_matches(movie_name, '([[:ascii:]]*)\s\(([\d]*)\)$') p(parts)
Here the regular expression says:
([[:ascii:]]*) - Capture all characters until the matches below
\s - Read past a space
\( - Read past an opening parenthesis
([\d]*) - Capture any digits
\) - Read past a closing parenthesis
$ - Match from the end of the string
So on input "Die Hard 17 (John lives forever) (2074)" it creates a string array with {'Die Hard 17 (John lives forever)', '2074'}. The scanning has to be from the end $, assuming all movie titles end with the year of publication in parentheses, in order to preserve parentheses and numbers in movie titles.
Now you can work on the movie genres. You have to split the string on the bar | using the regex_split_to_table() function and then join to the genre table on the genre name:
INSERT INTO moviegenre
SELECT movie_id, genre_id
FROM movies_csv, regexp_split_to_table(movie_genre, '\|') p(genre) -- escape the |
JOIN genre ON genre.genre_name = p.genre;
After all is done and dusted you can delete the movies_csv table.