4차 카테고리까지 만들었고,
1차 2차 3차 카테고리 클릭시 움직이는 스크립트를 각각 넣었어요.
n차 까지 알아서 때다 쓰시면 됩니당 ㅎ

itemform.php에서
카테고리 들고오는 부분은 conv_selected_option() & $category_select를 이용해서 넣으면 좋아요 ㅎ
어떤 소스가 들어가야 된다는 걸 나타내기 위해 그냥 소스로 넣었어요 ㅎ



itemform.php

<div id="cate1">
<select size="15" name="ca_id" id="caa_id" class="cid" >
	<?php
	$sql_ca_id1="SELECT ca_id, ca_name FROM g5_shop_category where length(ca_id) = '2' order by ca_id ";

	$result_ca_id1 = sql_query($sql_ca_id1);
	for($i=0; $row_ca_id1 = sql_fetch_array($result_ca_id1); $i++){
		?>
		<option value=<?php echo $row_ca_id1[ca_id]; ?> <?php if($row_ca_id1[ca_id] == substr($ca_id, 0, 2)) echo 'selected'?>><?php echo $row_ca_id1[ca_name]; ?></option>
	<?php } ?>
</select>
</div>

<div id="cate2" >
<?if($ca_id && strlen($ca_id) >= 4){?>
<select size="15" name="ca_id" id="caa_id2" class="cid"  >
	<?php
	$sql_ca_id1="SELECT ca_id, ca_name FROM g5_shop_category where length(ca_id) = '4' order by ca_id ";

	$result_ca_id1 = sql_query($sql_ca_id1);
	for($i=0; $row_ca_id1 = sql_fetch_array($result_ca_id1); $i++){
		?>
		<option value=<?php echo $row_ca_id1[ca_id]; ?> <?php if($row_ca_id1[ca_id] == substr($ca_id, 0, 4)) echo 'selected'?>><?php echo $row_ca_id1[ca_name]; ?></option>
	<?php } ?>
</select>
<?php } ?>
</div>

<div id="cate3">
<?if($ca_id && strlen($ca_id) >= 6){?>
<select size="15" name="ca_id" id="caa_id3" class="cid" >
	<?php
	$sql_ca_id1="SELECT ca_id, ca_name FROM g5_shop_category where length(ca_id) = '6' order by ca_id ";

	$result_ca_id1 = sql_query($sql_ca_id1);
	for($i=0; $row_ca_id1 = sql_fetch_array($result_ca_id1); $i++){
		?>
		<option value=<?php echo $row_ca_id1[ca_id]; ?> <?php if($row_ca_id1[ca_id] == substr($ca_id, 0, 6)) echo 'selected'?>><?php echo $row_ca_id1[ca_name]; ?></option>
	<?php } ?>
</select>
<?php } ?>
</div>

<div id="cate4">
<?if($ca_id && strlen($ca_id) >= 8){?>
<select size="15" name="ca_id" id="caa_id4" class="cid" >
	<?php
	$sql_ca_id1="SELECT ca_id, ca_name FROM g5_shop_category where length(ca_id) = '8' order by ca_id ";

	$result_ca_id1 = sql_query($sql_ca_id1);
	for($i=0; $row_ca_id1 = sql_fetch_array($result_ca_id1); $i++){
		?>
		<option value=<?php echo $row_ca_id1[ca_id]; ?> <?php if($row_ca_id1[ca_id] == substr($ca_id, 0, 8)) echo 'selected'?>><?php echo $row_ca_id1[ca_name]; ?></option>
	<?php } ?>
</select>
<?php } ?>

<script>
	$(document).ready(function() {
		$(document).on("click", "#caa_id", function() {
			var company_is = $('#caa_id').val();
			$.ajax({
				url: '/adm/ajax.category_select.php',
				type: 'post',
				data: { ca_id: $('#caa_id').val() ,  length: $('#caa_id').val().length },
				success: function(result) {
					var data = JSON.parse(result);
					if(data.success == 0) {
						console.log(data.msg);
					}else{
						$('#cate2').css('display', 'block');
						$('#cate2').html(data.data);
						$('#cate3').html('');
						$('#cate4').html('');
					}
				}
			});
		});


		$(document).on("click", "#caa_id2", function() {
			 var company_is = $('#caa_id2').val();
			$.ajax({
				url: '/adm/ajax.category_select.php',
				type: 'post',
				data: { ca_id: $('#caa_id2').val() ,  length: $('#caa_id2').val().length },
				success: function(result) {
					var data = JSON.parse(result);
					if(data.success == 0) {
						console.log(data.msg);
					}else{
						$('#cate3').css('display', 'block');
						$('#cate3').html(data.data);
						$('#cate4').html('');
					}
				}
			});
		});
		$(document).on("click", "#caa_id3", function() {
			 var company_is = $('#caa_id3').val();
			$.ajax({
				url: '/adm/ajax.category_select.php',
				type: 'post',
				data: { ca_id: $('#caa_id3').val() ,  length: $('#caa_id3').val().length },
				success: function(result) {
					var data = JSON.parse(result);
					if(data.success == 0) {
						console.log(data.msg);
					}else{
						$('#cate4').css('display', 'block');
						$('#cate4').html(data.data);
					}
				}
			});
		});
	});
</script>

ajax.category_select.php

<?php
include_once('./_common.php');

if(!empty($_POST['ca_id'])){
	if($_POST['length']=='2'){
		$qry = "SELECT ca_id, ca_name FROM g5_shop_category WHERE ca_id like '".$_POST['ca_id']."%' and ca_id != '".$_POST['ca_id']."' and length(ca_id) = '4' ";
	}elseif($_POST['length']=='4'){
		$qry = "SELECT ca_id, ca_name FROM g5_shop_category WHERE ca_id like '".$_POST['ca_id']."%' and ca_id != '".$_POST['ca_id']."' and length(ca_id) = '6'  ";
	}elseif($_POST['length']=='6'){
		$qry = "SELECT ca_id, ca_name FROM g5_shop_category WHERE ca_id like '".$_POST['ca_id']."%' and ca_id != '".$_POST['ca_id']."' and length(ca_id) = '8'  ";
	}
}

$qid = sql_query($qry);
$num_rows = sql_num_rows($qid);

if($num_rows > 0) {

if($_POST['length']=='2'){
    $output = '<select name="ca_id" size="15" id="caa_id2"class="cid"  >';
}elseif($_POST['length']=='4'){
    $output = '<select name="ca_id" size="15" id="caa_id3"class="cid" >';
}elseif($_POST['length']=='6'){
    $output = '<select name="ca_id" size="15" id="caa_id4"class="cid" >';
}
    for ($i = 0; $row = sql_fetch_array($qid); $i++)
    {
        $output .= '<option value="'.$row['ca_id'].'">'.$row['ca_name'].'</option>';
    }
    $output .= '</select>';
    exit(json_encode(array('success' => '1', 'data' => $output,'site'=>$_POST['ca_id'])));
} else {
   die(json_encode(array('success' => '0', 'msg' => '하위 카테고리가 없습니다. ')));
}
?>