SQL update value for checkbox

I have this code where I can add and later on update multiple checkbox. I can already add the value of the of checkbox into the database but I'm having problem when updating it. The value inserted into the database for checkbox is either 1 or 0.

Insert HTML code :

<tr>
  <td align="center" width="150"><input type="hidden" name="leave_al" value="0" />
                                 <input type="checkbox" name="leave_al" value="1">Annual Leave </td>
  <td align="center" width="150"><input type='text' size='15' name='annual_days' id='annual_days'> day(s) </td>
</tr> 

<tr>
  <td align="center" width="150"><input type="hidden" name="leave_matl" value="0" />
                                 <input type="checkbox" name="leave_matl" value="1">Maternity Leave </td>
  <td align="center" width="150"><input type='text' size='15' name='maternity_days' id='maternity_days'> day(s) </td>
</tr>

Update HTML code :

<?php 
        if ($row2['leave_al'] == 1)
        {
            echo "<td><input type='checkbox' name='leave_al' value='1' checked> Annual Leave </td>";
        }
        else
        {
            echo "<td><input type='checkbox' name='leave_al' value='0'> Annual Leave </td>";
        }

        if ($row2['leave_matl'] == 1)
        {
            echo "<td><input type='checkbox' name='leave_matl' value='1' checked> Maternity Leave </td>";
        }
        else
        {
            echo "<td><input type='checkbox' name='leave_matl' value='0'> Maternity Leave </td>";
        }
    ?>           

Update process code :

if(isset($_POST['update']))
{
    $leave_al = ($_POST['leave_al']=="1"?1:0);
    $leave_matl = ($_POST['leave_matl']=="1"?1:0); 

    $query = "UPDATE leaves 
    SET leave_al = '".$leave_al."', leave_matl = '".$leave_matl."',
    WHERE emp_id= '$id'";
}

Based on the coding above, when I checked the box, the value will be opposite. For example if I checked the box, the value will be 0 in the database. Something seems wrong about this code.

A lot of examples I've seen showed on how to update with array. If you could help me guide the correct way to update the checkbox and changed the 1 0 value. Thanks!