SQL-错误代码1005，错误号为121

Question

我正在运行以下由 MySQL Workbench 自动生成的MySQL脚本（已精简），出现以下错误：

1005无法创建表“ regula.reservation”（错误号：121）

我对数据库不是很精通，并且此错误也不是非常有用。
这里有什么问题？

-- -----------------------------------------------------
-- Table `regula`.`Users`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `regula`.`Users` ;

CREATE  TABLE IF NOT EXISTS `regula`.`Users` (
  `idUsers` INT UNSIGNED NOT NULL AUTO_INCREMENT ,
  `name` TEXT NOT NULL ,
  `type` TEXT NOT NULL ,
  `pwd` TEXT NOT NULL ,
  PRIMARY KEY (`idUsers`) ,
  UNIQUE INDEX `idUsers_UNIQUE` (`idUsers` ASC) )
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `regula`.`Projects`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `regula`.`Projects` ;

CREATE  TABLE IF NOT EXISTS `regula`.`Projects` (
  `idProjects` INT UNSIGNED NOT NULL AUTO_INCREMENT ,
  `ownerId` INT UNSIGNED NOT NULL ,
  `name` TEXT NOT NULL ,
  `date` DATE NOT NULL ,
  `time` TIME NOT NULL ,
  `place` TEXT NOT NULL ,
  `itemType` INT NOT NULL ,
  PRIMARY KEY (`idProjects`) ,
  UNIQUE INDEX `idProjects_UNIQUE` (`idProjects` ASC) ,
  INDEX `ownerId` (`ownerId` ASC) ,
  CONSTRAINT `ownerId`
    FOREIGN KEY (`ownerId` )
    REFERENCES `regula`.`Users` (`idUsers` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `regula`.`ItemTypes`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `regula`.`ItemTypes` ;

CREATE  TABLE IF NOT EXISTS `regula`.`ItemTypes` (
  `idItemTypes` INT UNSIGNED NOT NULL ,
  `prjId` INT UNSIGNED NOT NULL ,
  `parentId` INT UNSIGNED NULL DEFAULT NULL ,
  `name` TEXT NOT NULL ,
  PRIMARY KEY (`idItemTypes`) ,
  INDEX `prjId` (`prjId` ASC) ,
  INDEX `parentId` (`parentId` ASC) ,
  CONSTRAINT `prjId`
    FOREIGN KEY (`prjId` )
    REFERENCES `regula`.`Projects` (`idProjects` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `parentId`
    FOREIGN KEY (`parentId` )
    REFERENCES `regula`.`ItemTypes` (`idItemTypes` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;


-- -----------------------------------------------------
-- Table `regula`.`Reservation`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `regula`.`Reservation` ;

CREATE  TABLE IF NOT EXISTS `regula`.`Reservation` (
  `idReservation` INT UNSIGNED NOT NULL AUTO_INCREMENT ,
  `prjId` INT UNSIGNED NOT NULL ,
  `itemTypeId` INT UNSIGNED NOT NULL ,
  `userId` INT UNSIGNED NOT NULL ,
  PRIMARY KEY (`idReservation`) ,
  INDEX `prjId` (`prjId` ASC) ,
  INDEX `itemTypeId` (`itemTypeId` ASC) ,
  INDEX `userId` (`userId` ASC) ,
  CONSTRAINT `prjId`
    FOREIGN KEY (`prjId` )
    REFERENCES `regula`.`Projects` (`idProjects` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `itemTypeId`
    FOREIGN KEY (`itemTypeId` )
    REFERENCES `regula`.`ItemTypes` (`idItemTypes` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `userId`
    FOREIGN KEY (`userId` )
    REFERENCES `regula`.`Users` (`idUsers` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

Answer 1

错误121表示存在外键约束错误。由于您使用的是InnoDB，因此您可以SHOW ENGINE INNODB STATUS在运行失败的查询后使用，以在本LATEST FOREIGN KEY ERROR节中获得解释。我自己运行了SQL，我得到了：

------------------------
LATEST FOREIGN KEY ERROR
------------------------
101210 14:55:50 Error in foreign key constraint creation for table `regula`.`Reservation`.
A foreign key constraint of name `regula`.`prjId`
already exists. (Note that internally InnoDB adds 'databasename'
in front of the user-defined constraint name.)
Note that InnoDB's FOREIGN KEY system tables store
constraint names as case-insensitive, with the
MySQL standard latin1_swedish_ci collation. If you
create tables or databases whose names differ only in
the character case, then collisions in constraint
names can occur. Workaround: name your constraints
explicitly with unique names.

基本上，您需要在最后一个表中给prjId约束名称一个唯一的名称。约束/外键名称是数据库的全局名称，因此不能在不同的表中重复使用。只需更改最后一个

  CONSTRAINT `prjId`

至

  CONSTRAINT `prjId2`