我想将数组中的字段数据库相互链接，然后显示信息

Question

Please Read this carefully so you understand the question. This question is for an assignment in University.

There are two tables, one is an Answer table and the other is a StudentAnswer table. There are 6 fields I am interested in, 4 in Answer table and 2 from StudentAnswer table. Below are tables and their fields and data.

Answer Table:

  QuestionId     AnswerId    AnswerContent   AnswerCorrect
   1             1           Leeds                1 (true)
   2             2           Manchester           0 (false)
   3             3           Birmingham           0 (false)

StudentAnswer Table:

    StudentAnswer  QuestionId
        2                1
        3                1
        1                1

(StudentAnswer field contain AnswerId's, these are student answers depending on which answer they selected for which question)

Now these fields and other fields are stored in an array which are displayed in a table. PHP code for this is below:

<table border='1'>
      <tr>
      <th>Session ID</th>
      <th>Question Number</th>
      <th>AnswerContent</th>
      <th>StudentAnswer</th>
      <th>Student ID</th>
      </tr>
      <?php

        while ($row = mysql_fetch_array($result)) {

            echo "
      <tr>
      <td>{$row['SessionId']}</td>
      <td>{$row['QuestionNo']}</td>
      <td>{$row['AnswerContent']}</td>
      <td>{$row['StudentAnswer']} </td>
      <td>{$row['StudentId']}</td>
      </tr>";
        }
      ?>
    </table>

I created a query which only displays only the correct answer (This is AnswerId where AnswerCorrect = 1) and it shows StudentAnswer so we can see what students have put down for their awnser to a particular question.

I want the query to output one row per question with the text of the student's answer (but does have to be the correct answer)

Below is query:

SELECT * FROM Question q
    INNER JOIN StudentAnswer sa ON q.QuestionId = sa.QuestionId
    JOIN Answer a ON sa.QuestionId = a.QuestionId  
WHERE
    (CorrectAnswer = '1')
ORDER BY $orderfield ASC";

The problem is that StudentAnswer is shown in int form and I want to show it in word form and the only way to do that is link to AnswerContent field. The problem is that if I just use $row['AnswerContent'], it displays the word answer for AnswerId which is fine but it doesn't do it for StudentAnswer. So my question is how can I do it so that I can display StudentAnswer as word form by linking it with AnswerContent?

I tried $row['StudentAnswerContent'] == $row['StudentAnswer'] = $row['AnswerContent']; but this backfired completley. Can you figure this out for me and show me example on how to achieve this.

I like to say that the problem is NOT the query. The query works fine. I want you to look at the $row['...'] section and tell me how can I link StudentAnswer and AnswerContent together so that it recognises what the correct AnswerContent is for each StudentAnswer.

Below shows what it outputs at moment from the query and array:

Session ID  Question Number   AnswerContent     StudentAnswer    Student ID       
 ABB          1               Leeds                  1           u0867587   
 ABB          1               Leeds                  3           u1231231

Below is what I really want to output:

Session ID  Question Number   AnswerContent     StudentAnswer     Student ID       
     ABB          1           Leeds               Leeds            u0867587   
     ABB          1           Leeds               Birmingham       u1231231

Row 1 shows what student u0867587 has put for his answer for question 1. The correct answer is leeds and he put for his answer leeds. Row 2 shows that student u1231231 answered the same question, obviously the correct answer is still leeds but he selected birmingham.

Thank You and any help will be much appreciated

Full code with solution of the query and the form submitted to output the result:

<form action="exam_QA.php" method="post" name="sessionform">        <!-- This will post the form to its own page"-->
      <p>Session ID: <input type="text" name="sessionid" value="<?php echo $sessionid; ?>" /></p>      <!-- Enter Session Id here-->
      <p>Question Number: <input type="text" name="questionno" value="<?php echo $questionno; ?>" /></p>      <!-- Enter Question Number here-->
      <p>Student Username: <input type="text" name="studentid" value="<?php echo $studentid; ?>" /></p>      <!-- Enter User Id here-->
      <p>Order Results By:
        <select name="orderfield">
          <option value="ordersessionid"<?php if ($orderfield == 'q.SessionId') echo ' selected="selected"' ?>>Session ID</option>
          <option value="orderquestionno"<?php if ($orderfield == 'q.QuestionNo') echo ' selected="selected"' ?>>Question Number</option>
          <option value="orderstudentid"<?php if ($orderfield == 'sa.StudentId') echo ' selected="selected"' ?>>Student Username</option>
          <option value="orderwhole"<?php if ($orderfield == 'q.SessionId AND q.QuestionNo') echo ' selected="selected"' ?>>Session ID and Question Number</option>
        </select>
      </p>
      <p><input type="submit" value="Submit" name="submit" /></p>
    </form>

    <?php
      if (isset($_POST['submit'])) {

        $query = "
         SELECT *, a2.AnswerContent as StudentAnswerContent
         FROM Question q
        INNER JOIN StudentAnswer sa ON q.QuestionId = sa.QuestionId
        LEFT JOIN Answer a ON (sa.QuestionId = a.QuestionId AND a2.CorrectAnswer = 1) 
        LEFT JOIN Answer a2 ON (sa.QuestionId = a2.QuestionId AND a2.AnswerId = sa.StudentAnswer) 
          WHERE
            ('".mysql_real_escape_string($sessionid)."' = '' OR q.SessionId = '".mysql_real_escape_string($sessionid)."')
          AND
            ('".mysql_real_escape_string($questionno)."' = '' OR q.QuestionNo = '".mysql_real_escape_string($questionno)."')
          AND
            ('".mysql_real_escape_string($studentid)."' = '' OR sa.StudentId = '".mysql_real_escape_string($studentid)."')
          ORDER BY $orderfield ASC";

Answer 1

SQL:

SELECT 
    q.* ,
    sa.*,
    a.*,
    a2.AnswerContent as StudentAnswerContent
FROM 
    Question q
INNER JOIN 
    StudentAnswer sa ON q.QuestionId = sa.QuestionId
LEFT JOIN 
    Answer a ON (sa.QuestionId = a.QuestionId AND a2.CorrectAnswer = 1) 
LEFT JOIN
    Answer a2 ON (sa.QuestionId = a2.QuestionId AND a2.AnswerId = sa.StudentAnswer)
ORDER BY $orderfield ASC";

Row:

$row['StudentAnswerContent']

Explanation:

1st join - u get student answer

2nd join - u get correct answer content

3rd join - u get student answer content

Answer 2

Your query isn't quite right. You need another join to the Answer table using StudentAnswer to get the text. Something like this should do it..

SELECT 
    SessionId,
    q.QuestionNumber,
    a.AnswerContent,
    a2.AnswerContent as StudentAnswerContent,
    StudentId
FROM Question q
    INNER JOIN StudentAnswer sa ON q.QuestionId = sa.QuestionId
    JOIN Answer a ON sa.QuestionId = a.QuestionId  
    JOIN Answer a2 ON sa.StudentAnswer = a2.AnswerId
WHERE
    (CorrectAnswer = '1')
ORDER BY $orderfield ASC";