My delete button is not functioning as expected - php

Question

I'm stuck in the delete function, I wonder why my delete button is not functioning, and I already edited my code.
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST")
{
$semester = ($_POST["semester"]);
$level = ($_POST["level"]);
}
?>
Here is the form method:
<form method="post" action="<?php echo($_SERVER["PHP_SELF"]);?>" enctype="multipart/form-data">
Here is to display the data in table form, and SELECT * is functioning
$sql = mysqli_query ($connection, "SELECT * FROM subject");
echo " <table>
<th>Semester</th>
<th>Level</th>
</tr>";
while($record = mysqli_fetch_assoc ($sql)){
echo "<tr>";
echo "<td>" . $record['semester'] . "</td>";
echo "<td>" . $record['level'] . "</td>";
echo "<td>" . "<input type=submit name=delete value=Delete>" . "</td>";
echo "</tr>";
}
This is the delete button code
if (isset($_POST['delete']))
{
$delete = mysqli_query ($connection, "DELETE FROM subject WHERE semester = '($_POST[semester])'");
}

Answer 1

Try this :
while($record = mysqli_fetch_assoc ($sql)){
echo "<tr>";
echo '<form action="mypage.php" method="post">';
echo "<td>" . $record['semester'] . "</td>";
echo "<td>" . $record['level'] . "</td>";
echo "<td>" . $record['course'] . "</td>";
echo "<td>" . $record['subject'] . "</td>";
echo "<td>" . $record['section'] . "</td>";
// And add field form hidden
echo '<input type="hidden" name="semester" value="'.$record['semester'].'">';
echo "<td>" . '<input type="submit" name="delete" value="Delete">' . "</td>";
echo "</form>";
echo "</tr>";
}
if (isset($_POST['delete']) && isset($_POST['semester']))
{
$stmt = $connection->prepare('DELETE FROM subject WHERE semester = ?');
// if $_POST['semester'] is integer else see http://php.net/manual/en/mysqli-stmt.bind-param.php
$stmt->bind_param('i', $_POST['semester']);
$stmt->execute();
}