Question

我希望在删除其ID时删除数据库中主题的全部内容。

if(isset($_GET['subject_id'])){
$subject_id = $_GET['subject_id'];}

$deleteexams = mysql_query("SELECT * FROM exam_exams where exam_subject_id = '$subject_id'")or die(mysql_query());
while($ids = mysql_fetch_array($deleteexams)){
$selected = $ids['exam_id'];
}
$deletequestions = mysql_query("SELECT * FROM exam_questions where question_exam_id = '$selected'")or die(mysql_query());
while($ids2 = mysql_fetch_array($deletequestions)){
$selectedids = $ids2['question_id'];
}
$deleteanswers = mysql_query("SELECT * FROM exam_answers where answer_question_set_id = '$selectedids'")or die(mysql_query());
while($ids3 = mysql_fetch_array($deleteanswers)){
$selectedidsans = $ids3['answer_id'];
}

     /// I want to delete all of the answers inside the questions of the exams in the subject  
    mysql_query("DELETE * FROM exam_answers where answer_id = '$selectedidsans'")or die(mysql_error());
    /////i want to delete all the questions
        mysql_query("DELETE * FROM exam_questions where answer_id = '$selectedids'")or die(mysql_error());
    ////this will work because this has the subject ids
        mysql_query("DELETE * FROM exam_exams where exam_subject_id = '$subject_id'")or die(mysql_error());
    /////and this too
        mysql_query("DELETE * FROM exam_subjects where subject_id = '$subject_id'")or die(mysql_error());

我的问题是如何删除答案和问题，因为它的字段中没有subject_id。

Answer 1

删除*来的语法不正确。

您确实需要使用评论中提到的IN，因为您可以使用考试ID选择表格中的所有answer_id，字段名称可能会根据您的情况而改变，但逻辑将是

   DELETE
FROM exam_answers
WHERE answer_id IN
    (SELECT answer_id
     FROM questions
     WHERE question_id IN
         (SELECT exam_id
          FROM exams
          WHERE subject_id=<yoursubjectid>))

不是一种有效的方法，实际上你可能最好在每个表中存储主题id，即使它是多余的

Answer 2

将IN与子查询一起使用也是我的第一个选择，但这里也是其他一些选项。

你在mysql表中使用外键吗？你可以让mysql通过参照完整性和级联来解决这个问题。看这里：MySQL foreign key constraints, cascade delete

如果您只查看PHP解决方案，则应首先从使用外键的表中删除记录。例如。首先删除考试科目，问题和答案，然后删除考试本身。

另一个选择是根本不删除记录（如果你需要某种考试历史记录）。您可以将这些记录标记为已删除或未激活，并在以后从数据库中选择数据时对其进行过滤。像这样：SELECT * FROM exam_exams where active = 1;

您能为我们提供您的mysql创建表脚本或ERA图吗？

使用具有不同表的ID删除数据库中的多个值

2 个答案: