php - 未成功使用 JOIN 查询 MySQL 数据库与 PHP

Question

这是我的数据库架构:

user
*user_id
*username
*password
*etc

quiz_response
*response_id
*user_id
*question_id
*response
*is_correct
*answer_time

question_choice
*choice_id
*question_id
*is_correct
*choice (VARCHAR)

question
*question_id
*quiz_id
*question (VARCHAR)

quiz
*quiz_id
*title (VARCHAR)

我正在使用 PHP 构建测验网络应用程序，但遇到了问题。目前，我正在尝试——没有运气——这个查询，我知道问题出在哪里，我只是不知道如何解决它。因此，为什么我会在 S.O.

// Grab the response data from the database to generate the form
    $query = "SELECT qr.response_id AS r_id, qr.question_id, qr.response, q.question, quiz.title " . 
        "FROM quiz_response AS qr " . 
        "INNER JOIN question AS q USING (question_id) " . 
        "INNER JOIN quiz USING (quiz_id) " . 
        "WHERE qr.user_id = '" . $_SESSION['user_id'] . "'";
    $data = mysqli_query($dbc, $query) or die("MySQL error: " . mysqli_error($dbc) . "<hr>\nQuery: $query"); 

在这一点上，我觉得我的第二个内部连接(INNER JOIN quiz USING (quiz_id))是问题所在。当我不包含此行并从查询中删除 quiz.title 时，它​​会起作用。所以，我的问题是如何维护原子数据库架构，同时仍然根据表“question”中的 quiz_id 获取测验标题？任何帮助将不胜感激!

Answer 1

我认为问题在于 quiz_id 不在 quiz_response 中。我使用 ON 关键字。尝试:

// Grab the response data from the database to generate the form
$query = "SELECT qr.response_id AS r_id, qr.question_id, qr.response, q.question, 
          quiz.title " . 
         "FROM quiz_response AS qr " . 
         "INNER JOIN question AS q ON (q.question_id = qr.question_id) " . 
         "INNER JOIN quiz ON (quiz.quiz_id = q.quiz_id) " . 
         "WHERE qr.user_id = '" . $_SESSION['user_id'] . "'";
$data = mysqli_query($dbc, $query) or 
         die("MySQL error: " . mysqli_error($dbc) . "<hr>\nQuery: $query");