title: Why do I keep getting a 1215 cannot add foreign key constraint error?
body: <pre><code>USE ccva1;
  
  CREATE TABLE art_piece(
  art_inventory_id INT(10) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  artist_id INT(11) NOT NULL, 
  gallery_id INT(11) NOT NULL, 
  art_collection VARCHAR(4) NOT NULL, 
  art_genre VARCHAR(50)NOT NULL, 
  art_title VARCHAR(50)NOT NULL, 
  art_medium VARCHAR(50)NOT NULL, 
  art_acquired VARCHAR(200)NOT NULL,
  art_date_acquired INT(10)NOT NULL, 
  art_appraisal_value VARCHAR(20), 
  art_size_inches VARCHAR(65),
  art_size_centimeters VARCHAR(50), 
  art_image VARCHAR(500)NOT NULL, 
  art_modified_by VARCHAR(30) NOT NULL,
  art_modified_date VARCHAR(30),
  INDEX art_piece_ind(artist_id), 
  FOREIGN KEY (artist_id) 
  REFERENCES artist(artist_id) 
  ON DELETE CASCADE, 
  INDEX art_piece1_ind(gallery_id), 
  FOREIGN KEY (gallery_id)
  REFERENCES gallery(gallery_id) 
  ON DELETE CASCADE,
  INDEX art_piece2_ind(artist_id), 
  FOREIGN KEY (art_modified_by) 
  REFERENCES admin(admin_user_name) 
  ON DELETE CASCADE )
  ENGINE = INNODB;
  
  
  
  
  CREATE TABLE art_exhibition(exhibition_id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  gallery_id INT(11) NOT NULL,
  exhibition_name VARCHAR(200) NOT NULL, 
  exhibition_date VARCHAR(60) NOT NULL,
  exhibition_time VARCHAR(30) NOT NULL, 
  exhibition_description VARCHAR(3000) NOT NULL, 
  exhibition_image VARCHAR(65) NOT NULL,
  exhibition_modified_by VARCHAR(30)NOT NULL, 
  exhibition_modified_date VARCHAR(30),
  INDEX gal_ind(gallery_id),
  FOREIGN KEY (gallery_id) 
  REFERENCES gallery(gallery_id),
  INDEX artist_ind(artist_id),
  FOREIGN KEY (artist_id) 
  REFERENCES artist(artist_id),
  CONSTRAINT admin_unique UNIQUE (admin_user_name)
  ) ENGINE = INNODB;
  </code></pre>