MySQL Errno 121，写入或更新时重复键？

Errno 121, duplicate key on write or update?

提问by artem

SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0;
SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0;
SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL,ALLOW_INVALID_DATES';

CREATE SCHEMA IF NOT EXISTS `mydb` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci ;
USE `mydb` ;

-- -----------------------------------------------------
-- Table `mydb`.`restaurants`
-- -----------------------------------------------------
CREATE  TABLE IF NOT EXISTS `mydb`.`restaurants` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `name` VARCHAR(128) NOT NULL ,
  `description` VARCHAR(1024) NOT NULL ,
  `address` VARCHAR(1024) NOT NULL ,
  `phone` VARCHAR(16) NOT NULL ,
  `url` VARCHAR(128) NOT NULL ,
  `min_order` INT NOT NULL ,
  `food_types` SET('pizza', 'sushi', 'osetian_pie') NOT NULL ,
  PRIMARY KEY (`id`) ,
  UNIQUE INDEX `name_UNIQUE` (`name` ASC) ,
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) )
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `mydb`.`regions`
-- -----------------------------------------------------
CREATE  TABLE IF NOT EXISTS `mydb`.`regions` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `restaurant` INT NOT NULL ,
  `name` VARCHAR(128) NOT NULL ,
  PRIMARY KEY (`id`) ,
  INDEX `restaurant_idx` (`restaurant` ASC) ,
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) ,
  CONSTRAINT `restaurant`
    FOREIGN KEY (`restaurant` )
    REFERENCES `mydb`.`restaurants` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `mydb`.`food`
-- -----------------------------------------------------
CREATE  TABLE IF NOT EXISTS `mydb`.`food` (
  `id` INT NOT NULL ,
  `type` ENUM('pizza', 'sushi', 'osetian_pie') NOT NULL ,
  `name` VARCHAR(45) NOT NULL ,
  `ingredients` VARCHAR(256) NULL ,
  `image` VARCHAR(256) NOT NULL ,
  PRIMARY KEY (`id`) ,
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) )
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `mydb`.`food_variant`
-- -----------------------------------------------------
CREATE  TABLE IF NOT EXISTS `mydb`.`food_variant` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `size` VARCHAR(16) NOT NULL ,
  `weight` VARCHAR(16) NOT NULL ,
  `price` INT NOT NULL ,
  `food` INT NOT NULL ,
  `restaurant` INT NOT NULL ,
  PRIMARY KEY (`id`) ,
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) ,
  INDEX `food_idx` (`food` ASC) ,
  INDEX `restaurant_idx` (`restaurant` ASC) ,
  CONSTRAINT `food`
    FOREIGN KEY (`food` )
    REFERENCES `mydb`.`food` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `restaurant`
    FOREIGN KEY (`restaurant` )
    REFERENCES `mydb`.`restaurants` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;



SET SQL_MODE=@OLD_SQL_MODE;
SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS;
SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS;

Error is:
    Executing SQL script in server
    ERROR: Error 1005: Can't create table 'mydb.food_variant' (errno: 121)

I see no duplicate constraints. Where is it?

我没有看到重复的约束。它在哪里？

回答by Michael Berkowski

This is likely because you have named at least one constraint with the same identifier as a column:

这可能是因为您至少命名了一个与列具有相同标识符的约束：

/* You already have a column named `restaurant` in this table, 
   but are naming the FK CONSTRAINT `restaurant` also... */
CONSTRAINT `restaurant`
    FOREIGN KEY (`restaurant` )
    REFERENCES `mydb`.`restaurants` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)

Should use a different identifier for the constraint like fk_restaurantas in :

应该为约束使用不同的标识符，例如fk_restaurant：

CONSTRAINT `fk_restaurant`
    FOREIGN KEY (`restaurant` )
    REFERENCES `mydb`.`restaurants` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)

And same thing in the foodtable:

food表中也有同样的事情：

  /* Name it fk_food */
  CONSTRAINT `fk_food`
    FOREIGN KEY (`food` )
    REFERENCES `mydb`.`food` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  /* Name it fk_restaurant */
  CONSTRAINT `fk_restaurant`
    FOREIGN KEY (`restaurant` )
    REFERENCES `mydb`.`restaurants` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)

Those are the only three I see, but there could be others I missed.

这是我唯一看到的三个，但可能还有其他我错过了。

回答by blekione

This answer comes from the comment to the answerfrom @Michael Berkowski. I post it as an answer as it actually worked for me:

这个答案来自@Michael Berkowski对答案的评论。我将其发布为答案，因为它实际上对我有用：

I was getting the errno 121 even after changing the constraint names across multiple tables. The problem was that even across different tables you cannot have the same constraint name. I was using fk_entryidin table1and table2and had to change them to fk_table1_entryidand fk_table2_entryidrespectively to make it work.

即使在跨多个表更改约束名称后，我仍然收到 errno 121。问题是，即使跨不同的表，您也不能具有相同的约束名称。我是用 fk_entryid在table1和table2，不得不改变他们 fk_table1_entryid并fk_table2_entryid分别以使其正常工作。

回答by Peter Moses

All the answers above are superb but didn't solve my problem even after i dropped all my tables, but everything worked perfectly and the migration ran smoothly after i dropped my DB and created it again.... It seems the keys are cached and aren't cleared after tables are dropped.

上面的所有答案都很棒，但即使在我删除了所有表之后也没有解决我的问题，但是在我删除我的数据库并再次创建它之后一切都运行良好并且迁移顺利进行.... 似乎键被缓存并且删除表后不会清除。

Note: This is not an answer to the question but my experience that i felt might help another person.

注意：这不是问题的答案，而是我认为可能会帮助他人的经验。