MySQL试图删除所有不受外键约束的行

Question

好吧,这可能是一个非常简单的问题,但我恐怕几乎不知道MySQL,所以请忍受我.我只是试图从一个表中删除不受另一个表中的外键约束的每一行 - 一个特定的表,这里只涉及两个表.create语句看起来有点像:

CREATE TABLE  `testschema`.`job` (
  `Job_Id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `Comment` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`Job_Id`) USING BTREE,
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

CREATE TABLE  `ermieimporttest`.`jobassignment` (
  `JobAssignment_Id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `JobId` int(10) unsigned DEFAULT NULL,
  PRIMARY KEY (`JobAssignment_Id`),
  KEY `FK_jobassignment_1` (`JobId`),
  CONSTRAINT `FK_jobassignment_1` FOREIGN KEY (`JobId`) REFERENCES `job` (`Job_Id`),
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

我的任何SQL语句都是:

DELETE FROM job USING job INNER JOIN jobAssignment WHERE job.Job_Id != jobAssignment.JobId;

我认为这是正确的 - 它应该删除作业表中的每个作业,而作业作业中没有作业,因为它是外键.但是,当我尝试执行它时失败并出现以下错误:

无法删除或更新父行:外键约束失败(testdatabase.jobassignment,CONSTRAINT FK_jobassignment_1 FOREIGN KEY(JobId)REFERENCES job (Job_Id))

那么我做错了什么傻事呢？

编辑:像往常一样,我在帖子发布后几秒钟就找到了答案.我使用(完全不同的)查询:

DELETE FROM job WHERE Job_Id NOT IN (SELECT JobId FROM jobassignment) 

出于好奇,这是更好的方法吗？我最初的想法是否可行？如果是这样,它有什么问题？

Answer 1

DELETE FROM job USING job 
LEFT JOIN jobAssignment ON(job.Job_Id = jobAssignment.JobId)
WHERE jobAssignment.JobId IS NULL;

Answer 2

您可能需要一个子查询,不确定这是否适用于mySQL,但至少类似于:

DELETE FROM job
WHERE job.Job_Id NOT IN (
  SELECT JobId FROM jobAssignment
)