php mysqli删除发布的变量问题

I have the php block below being used to try to delete a posted variable $super. The "if" part of this statement runs and displays the variable that I am trying to remove But it shows the echo as {variable} with braces around it, which is why I think maybe the sql isn't working

<?php
    $sql="DELETE FROM `supervisors` WHERE supervisor_name='{$super}'";
    if (mysqli_query($conn, $sql))
    {
        echo "$super";
        echo "1 record removed";
    }
    else{   
        die('Error: ' .mysql_error());
    }
    mysqli_close($conn);
?>

Change this line

$sql="DELETE FROM `supervisors` WHERE supervisor_name='{$super}'";

to

$sql="DELETE FROM `supervisors` WHERE supervisor_name='$super'";