Possible to do a MySQL foreign key to one of two possible tables?

Question

Well here\'s my problem I have three tables; regions, countries, states. Countries can be inside of regions, states can be inside of regions. Regions are the top of the fo

Answer 1

Well, i have two tables:

1. songs

a) Song number b) Song title ....

2. playlists a) Playlist number b) Playlist title ...

and i have an third

3. songs_to_playlist_relation

The problem is that some kinds of playlists have link to other playlists. But in mysql we don't have foreign key that is associated with two tables.

My solution: I will put a third column in songs_to_playlist_relation. That column will be boolean. If 1 then song, else will link to the playlist table.

So:

3. songs_to_playlist_relation

a) Playlist_number (int) b) Is song (boolean) c) Relative number (song number or playlist number) (int) (not foreign key to any table)

 #create table songs
    queries.append("SET SQL_MODE = NO_AUTO_VALUE_ON_ZERO;")
    queries.append("CREATE TABLE songs (NUMBER int(11) NOT NULL,SONG POSITION int(11) NOT NULL,PLAY SONG tinyint(1) NOT NULL DEFAULT '1',SONG TITLE varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,DESCRIPTION varchar(1000) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,ARTIST varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT 'Άγνωστος καλλιτέχνης',AUTHOR varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT 'Άγνωστος στιχουργός',COMPOSER varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT 'Άγνωστος συνθέτης',ALBUM varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT 'Άγνωστο άλμπουμ',YEAR int(11) NOT NULL DEFAULT '33',RATING int(11) NOT NULL DEFAULT '5',IMAGE varchar(600) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,SONG PATH varchar(500) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,SONG REPEAT int(11) NOT NULL DEFAULT '0',VOLUME float NOT NULL DEFAULT '1',SPEED float NOT NULL DEFAULT '1') ENGINE=InnoDB DEFAULT CHARSET=utf8;")
    queries.append("ALTER TABLE songs ADD PRIMARY KEY (NUMBER), ADD UNIQUE KEY POSITION (SONG POSITION), ADD UNIQUE KEY TITLE (SONG TITLE), ADD UNIQUE KEY PATH (SONG PATH);")
    queries.append("ALTER TABLE songs MODIFY NUMBER int(11) NOT NULL AUTO_INCREMENT;")


#create table playlists
queries.append("CREATE TABLE `playlists` (`NUMBER` int(11) NOT NULL,`PLAYLIST POSITION` int(11) NOT NULL,`PLAYLIST TITLE` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,`PLAYLIST PATH` varchar(500) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8;")
queries.append("ALTER TABLE `playlists` ADD PRIMARY KEY (`NUMBER`),ADD UNIQUE KEY `POSITION` (`PLAYLIST POSITION`),ADD UNIQUE KEY `TITLE` (`PLAYLIST TITLE`),ADD UNIQUE KEY `PATH` (`PLAYLIST PATH`);")
queries.append("ALTER TABLE `playlists` MODIFY `NUMBER` int(11) NOT NULL AUTO_INCREMENT;")

#create table for songs to playlist relation
queries.append("CREATE TABLE `songs of playlist` (`PLAYLIST NUMBER` int(11) NOT NULL,`SONG OR PLAYLIST` tinyint(1) NOT NULL DEFAULT '1',`RELATIVE NUMBER` int(11) NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8;")
queries.append("ALTER TABLE `songs of playlist` ADD KEY `PLAYLIST NUMBER` (`PLAYLIST NUMBER`) USING BTREE;")
queries.append("ALTER TABLE `songs of playlist` ADD CONSTRAINT `playlist of playlist_ibfk_1` FOREIGN KEY (`PLAYLIST NUMBER`) REFERENCES `playlists` (`NUMBER`) ON DELETE RESTRICT ON UPDATE RESTRICT")

That's all!

playlists_query = "SELECT s1.*, s3.*, s4.* FROM songs as s1 INNER JOIN `songs of playlist` as s2 ON s1.`NUMBER` = s2.`RELATIVE NUMBER` INNER JOIN `playlists` as s3 ON s3.`NUMBER` = s2.`PLAYLIST NUMBER` INNER JOIN `playlists` as s4 ON s4.`NUMBER` = s2.`RELATIVE NUMBER` ORDER BY s3.`PLAYLIST POSITION`,`s1`.`SONG POSITION`"