Question

I find innodb quite annoying when I try to design a db structure, at least compared with MyIsam, which seems to have less limitations

Say, if I want to create a simple library system.
And I have four tables.

1,table book_item, which records the book_name, author, publish time and those basic information about books

2, table book, which represents a specific real object of the book item. So a book_item object can relate to many book objects.

3, table tag, which represents a book tag. Like science, literature, architecture and so on.

4, table tag_book_item_relation, which relates tags to book_items.

So, the relations are as below.

1,we have a book item to book is one-to-many relationship

2,book_item to tag is many-to-many relationship.

Note here, engine for the table are all innodb
If I try to create the tables, it will fail:

Error:
Executing SQL script in server
ERROR: Error 1005: Can't create table 'yet_another_test.book' (errno: 121)

However, if I change the engine of book or tag_book_item_relation to MyISAM, everything will be fine.

So, I am wondering what is going wrong if I use engine innodb for tablebook and tag_book_item_relation

The sql script is here(forward engineering in MySQL workbench):

CREATE  TABLE IF NOT EXISTS `yet_another_test`.`tag` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  PRIMARY KEY (`id`) ,
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) )
ENGINE = InnoDB;

CREATE  TABLE IF NOT EXISTS `yet_another_test`.`book_item` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  PRIMARY KEY (`id`) ,
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) )
ENGINE = InnoDB;

CREATE  TABLE IF NOT EXISTS `yet_another_test`.`tag_book_item_relation` (
  `book_item_id` INT NOT NULL ,
  `tag_id` INT NOT NULL ,
  PRIMARY KEY (`book_item_id`, `tag_id`) ,
  INDEX `fk_tag` (`tag_id` ASC) ,
  INDEX `fk_book_item` (`book_item_id` ASC) ,
  CONSTRAINT `fk_tag`
    FOREIGN KEY (`tag_id` )
    REFERENCES `yet_another_test`.`tag` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_book_item`
    FOREIGN KEY (`book_item_id` )
    REFERENCES `yet_another_test`.`book_item` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

CREATE  TABLE IF NOT EXISTS `yet_another_test`.`book` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `book_item_id` INT NOT NULL ,
  PRIMARY KEY (`id`, `book_item_id`) ,
  INDEX `fk_book_item` (`book_item_id` ASC) ,
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) ,
  CONSTRAINT `fk_book_item`
    FOREIGN KEY (`book_item_id` )
    REFERENCES `yet_another_test`.`book_item` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

Answer 1

Create your tables without the Foreign Key constraints. Although the same statements work with MyISAM engine, the constraints are silently ignored there – that is why you are not getting the errors. If you really need those constraints, then create them correctly. However, I generally tend to avoid FK constraints and implement the constraints at application level.

One problem I spot right away are the symbols of your constraints which have to be unique at DB level and you have fk_book_item both on tag_book_item_relation table and on book table