How to insert values in to the datbase based on checked and unchecked checkboxes

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PHP

My table name is Attendance.If the value of checkbox is checked then I have to insert 'P'(Present) otherwise I have to insert -1(Absent).

Fields of my table, Regno ,Name,Attendance.

How to use the condition in check box using php

What I have tried:

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checked=false;
function checkedAll (all) {var aa= document.getElementById('all'); if (checked == false)
{
checked = true
}
else
{
checked = false
}for (var i =0; i < aa.elements.length; i++){ aa.elements[i].checked = checked;}
}

  <?php

if(isset($_POST['insert']))
{

$ayear=$_POST['ayear'];
$course=$_POST['course'];
$year=$_POST['year'];
$sem=$_POST['sem'];
$section=$_POST['section'];
$day=$_POST['day'];
$hour=$_POST['hour'];
$dt=$_POST['dt'];
$subject=$_POST['subject'];
$attendance=$_POST['attendance'];
$lname=$_POST['lname'];

$sqlque=mysql_query("SELECT * FROM studentdetails WHERE courseid='$course' AND semester='$sem' AND section='$section' order by studid ") or die(mysql_error());
$sno=0; 
while(each($attendance))
{
$row=mysql_fetch_assoc($sqlque);
    $regno=$row['studid'];
	$atty=$attendance[$sno];

    $ins=mysql_query("INSERT INTO saa VALUES('$ayear','$dt','$year','$sem','$section','$course','$subject','$regno','$day','$lname','$atty','$hour')") or die(mysql_error());
    $sno++;
}
//echo $sno.' Records Inserted';

}
?>