MySQL工作台数据库错误

Question

我使用Mysql Qorkbench创建了一个数据库，并尝试将Engineer转发到数据库，但它完成时出现错误，消息为Log：

> Executing SQL script in server
ERROR: Error 1005: Can't create table `mydb`.`cds` (errno: 121 "Duplicate key on write or update")
SQL Code:
        -- -----------------------------------------------------
        -- Table `mydb`.`CDs`
        -- -----------------------------------------------------
        CREATE TABLE IF NOT EXISTS `mydb`.`CDs` (
          `CDid` INT NOT NULL AUTO_INCREMENT,
          `Titel` VARCHAR(45) NOT NULL,
          `Autor` VARCHAR(45) NOT NULL,
          `Erscheinungsjahr` VARCHAR(45) NOT NULL,
          `Genre` VARCHAR(45) NOT NULL,
          `Stockwerk` VARCHAR(45) NOT NULL,
          `Regal` INT NOT NULL,
          `Ausgeborgt` INT NULL,
          `Rezensionen` VARCHAR(600) NULL,
          `Kurzbeschreibung` VARCHAR(600) NOT NULL,
          PRIMARY KEY (`CDid`),
          UNIQUE INDEX `CDid_UNIQUE` (`CDid` ASC),
          INDEX `Buchungsid_idx` (`Ausgeborgt` ASC),
          CONSTRAINT `Buchungsid`
            FOREIGN KEY (`Ausgeborgt`)
            REFERENCES `mydb`.`Buchung` (`Buchungsid`)
            ON DELETE NO ACTION
            ON UPDATE NO ACTION)
        ENGINE = InnoDB

SQL script execution finished: statements: 9 succeeded, 1 failed

Fetching back view definitions in final form.
Could not get definition for mydb.view1 from server
1 views were read back.

这是我的Database的能效比图表

Answer 1

主键本质上是一个带索引的唯一非空值约束。您不需要添加额外的唯一约束，实际上也不能添加，正如错误所指定的那样。去掉额外的unique index子句，就可以了：

CREATE TABLE IF NOT EXISTS `mydb`.`CDs` (
  `CDid` INT NOT NULL AUTO_INCREMENT,
  `Titel` VARCHAR(45) NOT NULL,
  `Autor` VARCHAR(45) NOT NULL,
  `Erscheinungsjahr` VARCHAR(45) NOT NULL,
  `Genre` VARCHAR(45) NOT NULL,
  `Stockwerk` VARCHAR(45) NOT NULL,
  `Regal` INT NOT NULL,
  `Ausgeborgt` INT NULL,
  `Rezensionen` VARCHAR(600) NULL,
  `Kurzbeschreibung` VARCHAR(600) NOT NULL,
  PRIMARY KEY (`CDid`), -- no need for an extra index
  INDEX `Buchungsid_idx` (`Ausgeborgt` ASC),
  CONSTRAINT `Buchungsid`
    FOREIGN KEY (`Ausgeborgt`)
    REFERENCES `mydb`.`Buchung` (`Buchungsid`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB