创建动态 WHERE 子句时出现的 mysqli 警告

我正在尝试创建一个带有动态where子句的查询。查询有一个默认的 where 子句，无论从students and问题的下拉菜单中选择哪个选项，它都将始终检查SessionId = ?。

然后我有一个 php 代码，如果用户选择了单个学生或单个问题（或者换句话说，没有选择选项 All 在 2 个下拉菜单中的任何一个中选择student drop down menu or the user has not selected全部in the question drop down menu). If the全部"选项，那么它不会将这些参数添加到 WHERE 子句中。

无论如何，在尝试执行此操作时，我收到以下错误：

Warning: mysqli::prepare(): (42000/1064): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE q.SessionId = ?' at line 15 in ... on line 320 
Fatal error: Call to a member function bind_param() on a non-object in ... on line 322

我的问题是我需要在下面的 mysqli 和 php 代码中整理什么才能修复错误？

下面是带有注释的代码，用于显示错误所在的行号：

$selectedstudentanswerqry = "
SELECT
StudentAlias, StudentForename, StudentSurname, q.SessionId, 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, StudentMark
FROM Student s
INNER JOIN Student_Answer sa ON (s.StudentId = sa.StudentId)
INNER JOIN Student_Response sr ON (sa.StudentId = sr.StudentId)
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"]);
$parameterTypes = 'i';
// Check whether a specific student was selected
if($_POST["student"] !== 'All') {
    $where[] = 'sa.StudentId = ?';
    $parameters[] = $_POST["student"];
    $parameterTypes .= 'i';
}
// Check whether a specific question was selected
// NB: This is not an else if!
if($_POST["question"] !== 'All') {
    $where[] = 'q.QuestionId = ?';
    $parameters[] = $_POST["question"];
    $parameterTypes .= 'i';
}
$selectedstudentanswerqry .= "
GROUP BY sa.StudentId, q.QuestionId
ORDER BY StudentAlias, q.SessionId, QuestionNo
";
// 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); //line 320 error
    // You only need to call bind_param once
    $selectedstudentanswerstmt->bind_param($parameterTypes,implode($parameters)); //line 322 error
}


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