How can I add prepare statement in my comment printing system - php

Question

I'm currently building a system where users can write and read comments. So the comments will be inserted into database (the inserting part is already protected with the prepared statement), so now I want to add the prepared statement at the comment printing part too.
This is the comment inserting part
<?php
if (isset($_POST['submit'])) {
$nickname=$_POST['user_nickname'];
$email=$_POST['user_email'];
$comment=$_POST['cmt_text'];
$course=$_POST['user_course'];
$rating=$_POST['user_rating'];
$classof=$_POST['user_classof'];
$school_id=$_POST['id'];
$db="INSERT INTO comments(user_nickname,user_email,cmt_text,user_course,user_rating,school_id,user_classof) VALUES(?,?,?,?,?,?,?)";
$stmt=mysqli_stmt_init($con);
if(!mysqli_stmt_prepare($stmt,$db)){
echo "Data Error";
}else{
mysqli_stmt_bind_param($stmt,"ssssiii", $nickname,$email,$comment,$course,$rating,$school_id,$classof);
mysqli_stmt_execute($stmt);
}
header("location:Done.php");
exit;
}?>
And this is where I want to add prepared statements
<?php
$sql = "SELECT * FROM comments WHERE school_id=$sid ORDER BY Datetime DESC ";
$result = mysqli_query($con, $sql);
if (mysqli_num_rows($result) > 0) {
while ($row = mysqli_fetch_assoc($result)) {
?>
<div class="single-item">
<h4><?php echo $row['user_nickname']; ?></h4>
<p><?php echo $row['Datetime'];
?></p>
<p><b>Course</b> : <?php echo $row['user_course'];
?></p>
<p><b>Class of</b> <?php echo $row['user_classof'];
?></b></p>
<p><b>Rating : </b><?php echo $row['user_rating'];
?>/5</p>
<p><b>Comment : </b><?php echo $row['cmt_text'];
?></p>
</div>
<?php
}
}
?>
I have tried adding, but I got stuck when it comes to the part where I need to put the parameter, since I am printing out all the comments, how can I add the ? parameter?
By the way, $sid is a specific id for one school. There's more than a hundred schools in thecomments table. I put all the comments from every schools in one table.

Answer 1

Just create a function in which you will prepare the data.
function selectComments(mysqli $mysqli, ?int $schoolId = null): array
{
if ($schoolId) {
$stmt = $mysqli->prepare('SELECT * FROM comments WHERE school_id=? ORDER BY Datetime DESC');
$stmt->bind_param('s', $schoolId);
$stmt->execute();
$result = $stmt->get_result();
} else {
$result = $mysqli->query('SELECT * FROM comments ORDER BY Datetime DESC');
}
return $result->fetch_all(MYSQLI_ASSOC);
}
Then you can call it like this:
foreach(selectComments($con, $sid) as $row) {
// your HTML table
}