MYSQL无法更新父表-关系数据库设计，外键约束和级联更新/删除

Question

I have a very simple database design for managing TV shows:

1. Parent table: tv_shows . Primary key: show_id
2. Child table: seasons . Primary key: season_id , Foreign key: show_id
3. Child table: episodes . Primary key: episode_id , Foreign key: season_id

Table creation SQL:

     $sql = "DROP TABLE IF EXISTS ".$table_shows.";
        CREATE TABLE $table_shows (
          show_id int(11) NOT NULL,
          name varchar(120) DEFAULT NULL,
          PRIMARY KEY  (show_id),
          UNIQUE KEY  show_id_UNIQUE (show_id)
        ) $charset_collate;

        DROP TABLE IF EXISTS ".$table_seasons.";
        CREATE TABLE $table_seasons (
          season_id int(10) NOT NULL,
          show_id int(11) DEFAULT NULL,
          name varchar(120) DEFAULT NULL,
          PRIMARY KEY  (season_id),
          KEY seasons_ibfk_1 (show_id),
          CONSTRAINT  seasons_ibfk_1 FOREIGN KEY  (show_id) REFERENCES $table_shows (show_id) ON DELETE CASCADE ON UPDATE CASCADE
        ) $charset_collate;

        DROP TABLE IF EXISTS ".$table_episodes.";
        CREATE TABLE $table_episodes (
          episode_id int(10) NOT NULL,
          season_id int(10) DEFAULT NULL,
          name varchar(120) DEFAULT NULL,
          PRIMARY KEY  (episode_id),
          KEY  season_id (season_id),
          CONSTRAINT  episodes_ibfk_1 FOREIGN KEY  (season_id) REFERENCES $table_seasons (season_id)
        ) $charset_collate;";

What I want to happen is if a show was deleted from the tv_shows table, then the delete cascades, so the seasons and episodes are also deleted from their respective tables.

I can insert into these tables fine. But if I try and delete a row from the tv_shows table then I get an SQL error:

ERROR 1451: 1451: Cannot delete or update a parent row: a foreign key constraint fails

So where have I gone wrong with my FK constraints?

Answer 1

You need to add the ON DELETE CASCADE to the episodes as well. This ensures that they all follow each other into the bin.

CONSTRAINT  episodes_ibfk_1 
    FOREIGN KEY  (season_id) 
    REFERENCES $table_seasons (season_id)   
    ON DELETE CASCADE