Question

我有一张桌子user，一张桌子assignment和一张桌子candidation（有一个主要的，不是自然的一张），它有两个外键。它们都是1：nc，意味着不能总是有用户进行候选（用户删除）或分配（删除分配）。

现在我怎样才能避免在两个外键中使用NULL？

用户：

-- Table `Ressource-Management`.`user`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `Ressource-Management`.`user` (
  `iduser` INT UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '',
  `name_first` VARCHAR(50) NOT NULL COMMENT '',
  `name_last` VARCHAR(50) NOT NULL COMMENT '',
  `attendance` INT UNSIGNED NOT NULL COMMENT '',
  `can_own` TINYINT(1) NOT NULL DEFAULT 0 COMMENT '',
  PRIMARY KEY (`iduser`)  COMMENT '')
ENGINE = InnoDB;

ASSIGNMENT：

-- -----------------------------------------------------
-- Table `Ressource-Management`.`assignment`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `Ressource-Management`.`assignment` (
  `idassignment` INT UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '',
  `owner` INT UNSIGNED NOT NULL COMMENT '',
  `budget` INT UNSIGNED NOT NULL COMMENT '',
  `priority` TINYINT UNSIGNED NOT NULL DEFAULT 0 COMMENT '',
  `date_to` DATETIME NULL COMMENT '',
  PRIMARY KEY (`idassignment`)  COMMENT '',
  INDEX `fk_assignment_user_idx` (`owner` ASC)  COMMENT '',
  CONSTRAINT `fk_assignment_user`
    FOREIGN KEY (`owner`)
    REFERENCES `Ressource-Management`.`user` (`iduser`)
    ON DELETE RESTRICT
    ON UPDATE CASCADE)
ENGINE = InnoDB;

CANDIDATION：

-- -----------------------------------------------------
-- Table `Ressource-Management`.`candidation`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `Ressource-Management`.`candidation` (
  `idcandidation` INT UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '',
  `user_iduser` INT UNSIGNED NULL COMMENT '',
  `assignment_idassignment` INT UNSIGNED NULL COMMENT '',
  `date_from` DATETIME NOT NULL COMMENT '',
  `date_to` DATETIME NOT NULL COMMENT '',
  `status` LONGBLOB NULL DEFAULT offen COMMENT '',
  `message` VARCHAR(4096) NULL COMMENT '',
  PRIMARY KEY (`idcandidation`)  COMMENT '',
  INDEX `fk_user_has_assignment_assignment1_idx` (`assignment_idassignment` ASC)  COMMENT '',
  INDEX `fk_user_has_assignment_user1_idx` (`user_iduser` ASC)  COMMENT '',
  UNIQUE INDEX `user_assignment_UNIQUE` (`user_iduser` ASC, `assignment_idassignment` ASC)  COMMENT '',
  CONSTRAINT `fk_user_has_assignment_user1`
    FOREIGN KEY (`user_iduser`)
    REFERENCES `Ressource-Management`.`user` (`iduser`)
    ON DELETE SET NULL
    ON UPDATE CASCADE,
  CONSTRAINT `fk_user_has_assignment_assignment1`
    FOREIGN KEY (`assignment_idassignment`)
    REFERENCES `Ressource-Management`.`assignment` (`idassignment`)
    ON DELETE SET NULL
    ON UPDATE CASCADE)
ENGINE = InnoDB;

Answer 1

一个可能性是在删除时创建一个触发器，如果已经是另一个键NULL

，我将丢弃删除

我如何在mysql中避免在外键上有两个空值？

1 个答案: