如何在python中查询sqlite3中的4个表？

Question

Here are my tables. I get 0 rows return.

CREATE TABLE Artist (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    name    TEXT UNIQUE
);
CREATE TABLE Album (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    artist_id  INTEGER,
    title   TEXT UNIQUE
);
CREATE TABLE Genre (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    name    TEXT
);
CREATE TABLE Track (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    title TEXT  UNIQUE,
    album_id  INTEGER,
    genre_id INTEGER,
    len INTEGER, rating INTEGER, count INTEGER
);

Here my SQL code:

SELECT Track.title, Artist.name, Album.title, Genre.name 
FROM Track JOIN Genre JOIN Album JOIN Artist 
ON Track.genre_id = Genre.id and Track.album_id = Album.id 
WHERE Album.artist_id = Artist.id
ORDER BY Artist.name LIMIT 3

I appreciate your looking into this problem.

Answer 1

You code is correct sofar, but you need to fill the just created tables with records.

For example by running (untested):

INSERT INTO Artist (name) VALUES ('Artist 1'), ('Artist 2');
INSERT INTO Genre (name) VALUES ('Genre 1'), ('Genre 2');

INSERT INTO Album (title, artist_id) VALUES ('Title 1', 1);

INSERT INTO Track(title, album_id, 
    genre_id, len, rating, count) 
    VALUES ('Track 1', 1, 1, 0, 0, 0);

Also you should declare artist_id , album_id and genre_id columns as foreign keys .