Question

我正在尝试在mysql中运行此查询

UPDATE studentassessment sa SET sa.issubmitted=FALSE WHERE 
sa.studentassessmentid <> 
    (SELECT studentassessmentid FROM studentassessment sa1 WHERE 
    sa.StudentId=sa1.StudentId
    AND sa.AssessmentPeriodId=sa1.AssessmentPeriodId 
    ORDER BY sa1.studentassessmentid DESC LIMIT 0, 1) 
AND sa.studentid=568;

给了我这个错误

您无法在FROM子句
中为更新指定目标表'sa'

我发现了这类问题的数量，但它们是针对他们被问到的查询所特有的，所以对我没什么帮助，从其中一个答案中我试图改变这样的查询

UPDATE studentassessment sa SET issubmitted=FALSE WHERE 
sa.studentassessmentid <> 
    (
      SELECT studentassessmentid FROM 
        (
          SELECT studentassessmentid FROM studentassessment sa1 WHERE 
              sa.StudentId=sa1.StudentId
          AND sa.AssessmentPeriodId=sa1.AssessmentPeriodId 
          ORDER BY sa1.studentassessmentid DESC LIMIT 0, 1
         )  AS T
    )
AND sa.studentid=568;

然后我开始收到此错误

'where子句'中的未知列'sa.StudentId'

任何帮助？

修改

这也行不通

UPDATE studentassessment sa
INNER JOIN 
(SELECT studentassessmentid FROM studentassessment sa1 WHERE 
    sa.StudentId=sa1.StudentId
    AND sa.AssessmentPeriodId=sa1.AssessmentPeriodId 
    ORDER BY sa1.studentassessmentid DESC LIMIT 0, 1) T
ON sa.studentassessmentid<>T.StudentAssessmentId 
SET sa.issubmitted=0
WHERE sa.studentid=568;

Answer 1

MySQL has that limitation;你无法更新你选择的表格而且你什么都不做。

目前，您无法更新表并从子查询中的同一表中进行选择。

但是你可以这样做：

CREATE TEMPORARY TABLE studentassessmentids (
    `id` INT,
    PRIMARY KEY (`id`)
);

LOCK TABLE studentassessment WRITE;
INSERT INTO studentassessmentids (SELECT ... prepare your ids);

UPDATE studentassessment sa
SET sa.issubmitted=FALSE
WHERE sa.studentassessmentid NOT IN (
    SELECT id
    FROM studentassessmentids AS ids
    WHERE ids.id = sa.studentassessmentid
)

UNLOCK TABLES;
DROP TEMPORARY TABLE studentassessmentids;

我从我的头顶编写代码，所以它不能直接使用，但希望你能够采用这个想法。

如果您可以将查询重写为JOIN语句组，例如（来自mysql.com）：

UPDATE items,month SET items.price=month.price
WHERE items.id=month.id;

它应该可以工作，但我不知道如何在不编写难以理解的代码的情况下使用连接实现NOT IN。

Answer 2

找到答案

   UPDATE studentassessment dest,
    (
       SELECT studentassessmentid,assessmentperiodid 
        FROM studentassessment sa WHERE sa.studentid=568
        AND sa.studentassessmentid<>
            (
               SELECT studentassessmentid FROM studentassessment s 
                WHERE s.studentid=568 
                AND sa.assessmentperiodid=s.assessmentperiodid
                ORDER BY studentassessmentid DESC LIMIT 1
            )

    )src

    SET dest.issubmitted=FALSE 
    WHERE dest.studentassessmentid=src.studentassessmentid

您不能在FROM子句中为更新指定目标表''

2 个答案: