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⚡ Optimize quiz page N+1 query #13

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⚡ Optimize quiz page N+1 query #13

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34 changes: 28 additions & 6 deletions quiz_system_git/quiz.php
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@
$stmtCheck->execute(['username' => $roll_no, 'quizID' => $final_quiz_ID]);

//if user already did, redirect to index.php with error
if($stmtCheck->rowCount() > 0){
if($stmtCheck->fetch()){
$user_msg = 'Sorry, but '.$roll_no.', has already attempted the quiz, '.$quzz_name.'!';
header('location: index.php?user_msg='.urlencode($user_msg));
exit();
Expand Down Expand Up @@ -73,7 +73,9 @@
$stmtQ->bindValue(':limit', $total_questions, PDO::PARAM_INT);
$stmtQ->execute();

if ($stmtQ->rowCount() < 1) {
$questions = $stmtQ->fetchAll(PDO::FETCH_ASSOC);

if (count($questions) < 1) {
$user_msg = 'Hey, weird, but it seems there are no questions in this quiz!';
header('location: index.php?user_msg='.urlencode($user_msg));
exit();
Expand All @@ -82,8 +84,28 @@
//setting Question No. to 1 on quiz page(necessary due to rand() above)
$m_display_ID = 1;

// Gather question IDs
$questionIDs = array();
foreach ($questions as $q) {
$questionIDs[] = $q['question_id'];
}

// Fetch all answers for these questions
$answersByQuestion = array();
if (!empty($questionIDs)) {
// Create placeholders string (?,?,?)
$inQuery = implode(',', array_fill(0, count($questionIDs), '?'));
$stmtAns = $pdo->prepare("SELECT * FROM answers WHERE question_id IN ($inQuery)");
$stmtAns->execute($questionIDs);
$allAnswers = $stmtAns->fetchAll(PDO::FETCH_ASSOC);

foreach ($allAnswers as $ans) {
$answersByQuestion[$ans['question_id']][] = $ans;
}
}

//looping through the questions and adding them on the page
while($m_row = $stmtQ->fetch()){
foreach($questions as $m_row){
//initializing the options
$m_answers='';

Expand Down Expand Up @@ -116,15 +138,15 @@
}

//gathering options of the question here
$stmtAns = $pdo->prepare("SELECT * FROM answers WHERE question_id=:questionID ORDER BY rand()");
$stmtAns->execute(['questionID' => $m_question_id]);
$current_answers = isset($answersByQuestion[$m_question_id]) ? $answersByQuestion[$m_question_id] : array();
shuffle($current_answers); // Randomize answers order

$m_answers .= '<tr>
<td></td>
<td>
';
//adding html to individual options here
while($m_row2 = $stmtAns->fetch()){
foreach($current_answers as $m_row2){
//getting row attributes in variables
$m_answer = $m_row2['answer'];
$m_answer_ID = $m_row2['id'];
Expand Down