Php mysql-通过选择每个用户的名称来统计其状态

我有一个包含学生姓名、当前日期和时间及其状态的表，如下所示

约翰有三天缺席

简有两天缺席

我有这个代码，但它计算所有缺席，不为特定的用户，所以我想只显示约翰缺席日和简缺席日，如果我在下拉菜单中选择它

<?php
$sql = "SELECT student_name, count(status) as numberOfabsent FROM attendance WHERE status = 'Absent' GROUP BY student_name";
        $result = $db->prepare($sql);
        $result->execute();
        while ($row = $result->fetch()) 
        echo $row['numberOfabsent'];
 ?>

可能在末尾添加having子句，作为
在（'John'，'jane'）或where条件中包含学生名。可能
选择学生名，将（*）计数为numberOfEmission…
    <?php
             $sql = "SELECT *, count(status) as numberOfabsent FROM attendance WHERE status = 'Absent' GROUP BY student_name";
             $result = $db->prepare($sql);
             $result->execute();
             while ($row = $result->fetch()) {
             $numberOfabsent = $row['numberOfabsent'];
             $absdate = $row['timestamp'];
             echo "<tr><td><a href='" . $configs->getConfig('WEB_ROOT') . "admin/adminuseredit.php?usertoedit=" . $row['student_name'] . "'>" . $row['student_name'] . "</a></td>"
             . "<td><div class='shorten'><a href='" . $row['numberOfabsent'] . "'>" . $numberOfabsent  . " days</a></div></td><td>" . $absdate . "</td>"
             . "<td class='text-center'><div class='btn-group btn-group-xs'><a href='".$configs->getConfig('WEB_ROOT')."admin/adminuseredit.php?usertoedit=".$row['student_name']."' title='Edit' class='open_modal btn btn-default'><i class='fa fa-pencil'></i> View</a>";
             echo"</tr>";
             }
     ?>