AJAX数组到PHP不起作用

Question

I have a set of checkboxes. If you click them, bits of a SQL string should be send to a php file, when a button is clicked.

The checkbox setup looks as follows:

<input type="checkbox" class="checkboxes" name="checkb[]" value="SYSTEM LIKE '%system%'">

The ajax looks as follows:

$("#button1").click(function(e) {
    var category_id = {};
    category_id['checkboxvalue'] = $('.checkboxes:checked').serialize();
    $.ajax({
        type: "POST",
        url: "allgemein.php",
        data: category_id,
        success: function(response) {
            $("#resulttable").show().html(response);
        }
    });
});

In php i try to call them like this:

$strWhere = '1=1';

if(true === isset($_POST['checkb']) && 0 < sizeof($_POST['checkb']))
{
    $strWhere .= '(';
    foreach($_POST['checkb'] as $checkboxval)
    {
        $strWhere .= '"'.$checkboxval.'" OR ';
    }
    //remove last OR
    $strWhere = substring($strWhere, 0, -3);
    $strWhere .= ')';
}

$strWhere gets added to the WHERE clause of my SQL query.

Can someone say why this is not working? $strWhere is always 1=1, it never enters the if-loop... somehow I'm not calling the array correctly with $_POST['checkb'] and I just can't figure out why.