Question

I am having trouble with looping through data when selecting an All option in one or both of relevant drop down menus. It is not going through all the records and displaying them, it is only going trough one set of data. It is suppose to display details for each student and for each question they have participated in. But it is only showing one student and one question and that is all.

Below is what it should display:

But instead at the moment it is just displaying this:

I believe what is causing this problem is the dynamic WHERE clause I have set up. Below is how dynamic WHERE clause works:

• Compulsory WHERE condition of q.SessionId = ?
• If user selects single student from student drop down menu, then add AND sa.StudentId = ? to WHERE clause
• If user selects All students option from student drop down menu, then remove or do not display AND sa.StudentId = ? from WHERE clause
• If user selects single question from question drop down menu, then add AND q.QuestionId = ? to WHERE clause
• If user selects All questions option from question drop down menu, then remove or do not display AND q.QuestionId = ? from WHERE clause

I have three drop down menus (below is what they look like with sample data):

Session:

<select name="session" id="sessionsDrop">
<option value="26">POKUB1</option>
<option value="27">POKUB2</option>
</select>

Student:

<select name="student" id="studentsDrop">
<option value="0">All</option>
<option value="39">Luke Mcfadzen</option>
<option value="40">Chris Tucker</option>
</select>

Question:

<select name="question" id="questionsDrop">
<option value="0">All</option>
<option value="72">1</option>
<option value="73">2</option>
</select>

Don’t forget how the WHERE condition is suppose to work which I mentioned above in this question. Lets say the session chosen from session drop down menu is POKUB 1, drop down value: 26.

If you select a single student and a single question, then it displays the details correctly e.g.

• Student: Luke McFadzen – drop down value: 39
• Question: 1 – drop down value: 72

So WHERE condition is q.SessionId = 26 AND sa.StudentId = 39 AND q.QuestionId = 72.

But if I select an All option in either or both student and question drop down menu, then the output only displays one student and one question and for some strange reason it combines answers from all questions and combines all student answer answers into the single output.

Now All option in both drop down menus has a drop down value of 0, now 0 is not a value to select from database but we have stated in dynamic where clause that if a 0 value is chosen from a specific drop down menu, then remove the relevant condition from the WHERE clause, so for example:

• All students and single question (value 72) – WHERE q.SessionId
= 26 AND q.QuestionId = 72
• Single (value 39) student and All questions – WHERE q.SessionId
= 26 AND sa.StudentId = 39
• All students and All questions – WHERE q.SessionId = 26

THE ABOVE SCENARIOS ARE HAVING THE PROBLEMS

If I just left the query with a static WHERE clause WHERE q.SessionId = ? then it outputs the details correctly if I select All students and All Questions, but I need the query to work for all different possible options selected from the drop down menus and hence why I need a dynamic WHERE clause. How can I get it to work so the correct details are outputted?

Code:

    $selectedstudentanswerqry = "
        SELECT
        sa.StudentId, StudentAlias, StudentForename, StudentSurname, q.SessionId, 
        q.QuestionId, QuestionNo, QuestionContent, o.OptionType, q.NoofAnswers, 
        GROUP_CONCAT( DISTINCT Answer ORDER BY Answer SEPARATOR ',' ) AS Answer, r.ReplyType, QuestionMarks, 
        GROUP_CONCAT(DISTINCT StudentAnswer ORDER BY StudentAnswer SEPARATOR ',') AS StudentAnswer, ResponseTime, MouseClick, 
        (
        SELECT sum( StudentMark )
        FROM Student_Answer sta
        WHERE sa.StudentId = sta.StudentId
        AND sa.QuestionId = sta.QuestionId
        )StudentMark
        FROM Student st
        INNER JOIN Student_Answer sa ON (st.StudentId = sa.StudentId)
        INNER JOIN Student_Response sr ON (sa.StudentId = sr.StudentId) AND sa.QuestionId = sr.QuestionId
        INNER JOIN Question q ON (sa.QuestionId = q.QuestionId)
        INNER JOIN Answer an ON q.QuestionId = an.QuestionId
        LEFT JOIN Reply r ON q.ReplyId = r.ReplyId
        LEFT JOIN Option_Table o ON q.OptionId = o.OptionId
        ";

        // Initially empty
        $where = array('q.SessionId = ?');
        $parameters = array($_POST["session"]);
        $parameterTypes = 'i';


        //check if POST is empty

        // Check whether a specific student was selected
        $p_student = empty($_POST["student"])?'':$_POST["student"];

        switch($p_student){
        case 0:
            //dont' add where filters
            break;
        default:
            $where[] = 'sa.StudentId = ?';
            $parameters[] .= $_POST["student"];
            $parameterTypes .= 'i';
        }

        // Check whether a specific question was selected
        $p_question = empty($_POST["question"])?'':$_POST["question"];

        switch($p_question){
        case 0:
            //dont' add where filters
            break;
        default:
            $where[] = 'q.QuestionId = ?';
            $parameters[] .= $_POST["question"];
            $parameterTypes .= 'i';
        }

        // If we added to $where in any of the conditionals, we need a WHERE clause in
        // our query
        if(!empty($where)) {
            $selectedstudentanswerqry .= ' WHERE ' . implode(' AND ', $where);
            global $mysqli;
            $selectedstudentanswerstmt=$mysqli->prepare($selectedstudentanswerqry);
            // You only need to call bind_param once

            if (count($where) == 1) {
            $selectedstudentanswerstmt->bind_param($parameterTypes, $parameters[0]);
        }
        else if (count($where) == 2) {
            $selectedstudentanswerstmt->bind_param($parameterTypes, $parameters[0], $parameters[1]);
        }
        else if (count($where) == 3) {
            $selectedstudentanswerstmt->bind_param($parameterTypes, $parameters[0], $parameters[1], $parameters[2]);
        }

        }

        $selectedstudentanswerqry .= "
          GROUP BY sa.StudentId, q.QuestionId
          ORDER BY StudentAlias, q.SessionId, QuestionNo
        ";

    // get result and assign variables (prefix with db)
    $selectedstudentanswerstmt->execute(); 
    $selectedstudentanswerstmt->bind_result($detailsStudentId,$detailsStudentAlias,$detailsStudentForename,$detailsStudentSurname,$detailsSessionId,
    $detailsQuestionId,$detailsQuestionNo,$detailsQuestionContent,$detailsOptionType,$detailsNoofAnswers,$detailsAnswer,$detailsReplyType,$detailsQuestionMarks,
    $detailsStudentAnswer,$detailsResponseTime,$detailsMouseClick,$detailsStudentMark); 

    $selectedstudentanswerstmt->store_result();
    $selectedstudentanswernum = $selectedstudentanswerstmt->num_rows(); 

 while ($selectedstudentanswerstmt->fetch()) {

                //Check if the student data exist.
                if (!isset($questions[$detailsStudentId])) {
                    $questions[$detailsStudentId] = array(
                        'studentalias' => $detailsStudentAlias,
                        'studentforename' => $detailsStudentForename,
                        'studentsurname' => $detailsStudentSurname,
                        'questions' => array()
                    );
                }

                $questions[$detailsStudentId]['questions'][$detailsQuestionId] = array(
                    'questionno'=>$detailsQuestionNo,
                    'content'=>$detailsQuestionContent,
                    'optiontype'=>$detailsOptionType,
                    'noofanswers'=>$detailsNoofAnswers,
                    'answer'=>$detailsAnswer,
                    'replytype'=>$detailsReplyType,
                    'questionmarks'=>$detailsQuestionMarks,
                    'studentanswer'=>$detailsStudentAnswer,
                    'responsetime'=>$detailsResponseTime,
                    'mouseclick'=>$detailsMouseClick,
                    'studentmark'=>$detailsStudentMark
                );
            }

            $selectedstudentanswerstmt->close();

    foreach ($questions as $studentId => $studentData) {
        echo '<p>'.$studentData['studentalias'].' - '.$studentData['studentforename'].' '.$studentData['studentsurname'].'</p>';

        foreach ($studentData['questions'] as $questionId => $questionData) {
            echo '<p><strong>'.$questionData['questionno'].': '.$questionData['content'].'<br/>';
            echo $questionData['optiontype'].' - '.$questionData['noofanswers'].' - '.$questionData['answer'].' - '.$questionData['replytype'].' - '.$questionData['questionmarks'].'<br/>';
            echo $questionData['studentanswer'].' - '.$questionData['responsetime'].' - '.$questionData['mouseclick'].' - '.$questionData['studentmark'].'</strong></p>';
        }
    }

Below are the possible var_dumps for $_POST['student'] and $_POST['question']:

SINGLE STUDENT AND SINGLE QUESTION:

• Student: Chris Tucker – string(2) “40”
• Question: 1 – string(2) “72”

SINGLE STUDENT AND ALL QUESTIONS:

• Student: Chris Tucker – string(2) “40”
• Question: All – string(1) “0”

ALL STUDENTS AND SINGLE QUESTION:

• Student: All – string(1) “0”
• Question: 1 – string(1) “72”

ALL STUDENTS AND ALL QUESTIONS:

• Student: All – string(1) “0”
• Question: All – string(1) “0”

Below is example var_dump($questions); if I select All students and All questions:

array(1) { 
[39]=> array(4) { 
["studentalias"]=> string(8) "u4838229" 
["studentforename"]=> string(5) "Chris" 
["studentsurname"]=> string(6) "Tucker" 
["questions"]=> array(1) { 
[72]=> array(11) { 
["questionno"]=> int(1) 
["content"]=> string(14) "What is a RAM?" 
["optiontype"]=> string(3) "A-E" 
["noofanswers"]=> int(1) 
["answer"]=> string(7) "B,C,D,E" 
["replytype"]=> string(6) "Single" 
["questionmarks"]=> int(5) 
["studentanswer"]=> string(9) "A,B,C,D,E" 
["responsetime"]=> string(8) "00:00:07" 
["mouseclick"]=> int(1) 
["studentmark"]=> string(1) "2" } } } }

UPDATE:

If I keep the mysqli query using a static WHERE clause when it just checks for q.SessionId = ? only, then when I select the All options in etiher or both drop down menus, it outputs the results fine no problem, only wither the dynamic where clause which I need to include as user my be able to select an indivdual student and/or indivdiual question that the All options do not work properly. Below is working mysqli code when using static WHERE clause:

$selectedstudentanswerqry = "
    SELECT
    sa.StudentId, StudentAlias, StudentForename, StudentSurname, q.SessionId, 
    q.QuestionId, QuestionNo, QuestionContent, o.OptionType, q.NoofAnswers, 
    GROUP_CONCAT( DISTINCT Answer ORDER BY Answer SEPARATOR ',' ) AS Answer, r.ReplyType, QuestionMarks, 
    GROUP_CONCAT(DISTINCT StudentAnswer ORDER BY StudentAnswer SEPARATOR ',') AS StudentAnswer, ResponseTime, MouseClick, 
    (
    SELECT sum( StudentMark )
    FROM Student_Answer sta
    WHERE sa.StudentId = sta.StudentId
    AND sa.QuestionId = sta.QuestionId
    )StudentMark
    FROM Student st
    INNER JOIN Student_Answer sa ON (st.StudentId = sa.StudentId)
    INNER JOIN Student_Response sr ON (sa.StudentId = sr.StudentId) AND sa.QuestionId = sr.QuestionId
    INNER JOIN Question q ON (sa.QuestionId = q.QuestionId)
    INNER JOIN Answer an ON q.QuestionId = an.QuestionId
    LEFT JOIN Reply r ON q.ReplyId = r.ReplyId
    LEFT JOIN Option_Table o ON q.OptionId = o.OptionId
    LEFT JOIN Session_Taken sta ON (st.StudentId = sta.StudentId)
      WHERE q.SessionId = ?
      GROUP BY sa.StudentId, q.QuestionId
      ORDER BY StudentAlias, q.SessionId, QuestionNo
    ";
    global $mysqli;
$selectedstudentanswerstmt=$mysqli->prepare($selectedstudentanswerqry);
$selectedstudentanswerstmt->bind_param('i',$_POST['session']);
// get result and assign variables (prefix with db)
$selectedstudentanswerstmt->execute(); 
$selectedstudentanswerstmt->bind_result($detailsStudentId,$detailsStudentAlias,$detailsStudentForename,$detailsStudentSurname,$detailsSessionId,
$detailsQuestionId,$detailsQuestionNo,$detailsQuestionContent,$detailsOptionType,$detailsNoofAnswers,$detailsAnswer,$detailsReplyType,$detailsQuestionMarks,
$detailsStudentAnswer,$detailsResponseTime,$detailsMouseClick,$detailsStudentMark); 

Answer 1

The empty() considers a ‘0’ as empty http://php.net/manual/en/function.empty.php,
so in $p_student = empty($_POST["student"])?'':$_POST["student"]; $p_student is true when $_POST[“student”] is ‘0’… As a result, the case below is always ‘default’, so you should may be set $p_student as a ‘0’ if empty() and it should be ok…I think… ( Thats for both $p_student and $p_question of course…).
`

    $p_student = empty($_POST["student"])?0:$_POST["student"];  // Now if $_POST['student'] is either 0 or empty $p_student will be 0

    switch($p_student){
    case 0:
        //dont' add where filters
        break;
    default:
        $where[] = 'sa.StudentId = ?';
        $parameters[] .= $_POST["student"];
        $parameterTypes .= 'i';
    }

    // Check whether a specific question was selected
    $p_question = empty($_POST["question"])?0:$_POST["question"]; // Same here, if $_POST['question'] is either 0 or empty $p_question will be 0
    switch($p_question){
    case 0:
        //dont' add where filters
        break;
    default:
        $where[] = 'q.QuestionId = ?';
        $parameters[] .= $_POST["question"];
        $parameterTypes .= 'i';
    }`