jQuery checkbox won't update.

Here's my html:

    <tr>
        <td class="tg-031e"><input type="checkbox" name="sel_a" class="a_qual" data-id23="<?php echo $row["id"]; ?>"
        <?php if($row["a_qual"] == 1) { echo "checked='1'"; } ?>
        ></td>
        <td class="a" colspan="2" data-id3="<?php echo $row["id"]; ?>" contenteditable><?php echo $row["a"] ?></td>
    </tr>

Here's my jQuery:

$(document).on('change', '.a_qual', function(){  
    var id = $(this).data("id23"); 
    var a_qual = $("input[type='checkbox']").val();
    edit_data(id, a_qual, "a_qual"); 
    console.log('my message' + a_qual);
}); 

Here's my edit_data function:

    function edit_data(id, text, column_name)  
{  
    $.ajax({  
        url:"edit.php",  
        method:"POST",  
        data:{id:id, text:text, column_name:column_name},  
        dataType:"text",  
        success:function(data){   
            fetch_data();
        }  
    });  
}  

And here's my edit.php:

include_once("includes/connection.php");
$sql = "UPDATE questions SET ".$_POST['column_name']."='".$_POST['text']."' 
WHERE id='".$_POST['id']."'";

// echo $sql;
if(mysqli_query($connection, $sql))
{
    echo 'Data Inserted';
}

I don't know what I'm doing well enough to make this work and I'm really stumped after reading dozens of posts across the internet. For some reason, I can get it to change my database value to "1" and then it gets stuck there. In my database I have a column named "a_qual" to store the "quality" of the checkbox and it's set to a TINYINT. Can anyone figure out my problem?