รบกวนช่วยแนะนำ แก้ไขหน่อยครับ การรับค่าจากcheckboxแล้วหาrecord ที่ว่างเพื่อ update ค่า

<?
$nameD = $_POST[namedir];
$namedir = iconv('UTF-8','windows-874',$_POST[namedir]);
$detaildir = $_POST[detaildir];
$date_down = $_POST[date_down];
$hr_down = $_POST
;
$minn_down = $_POST[minn];
$date_job = date("Y-m-d");
$time_job = date("H-i-s");
$key_job = date("YmdHis");

include "connect.php";
include "check_sess.php";
$sql = "select * from tb_member ";
mysql_query("SET NAMES UTF8");
mysql_query("SET collection_connection='UTF8'");
$result = mysql_db_query($dbname,$sql);
$record = mysql_fetch_array($result);
$job_start = $record[job1];
$name = $record[name];

$make_dir = mkdir("$namedir $date_job");
if($make_dir){
	echo "<script> alert('สร้างระบบส่งงานเรื่อง $nameD เรียบร้อยแล้วครับ') </script>";
}else{
	echo "<script> alert('สร้างระบบส่งงานไม่ได้') </script>";
}

$result = mysql_db_query($dbname,$sql);
$sql = "insert into job_member values('','$nameD','$detaildir','$date_job','$date_down','$hr:$minn', '$key_job')";
mysql_query("SET NAMES UTF8");
mysql_query("SET collection_connection='UTF8'");
$result = mysql_query($sql);

function check_job($m){
	$sql = " select * from tb_member where username = '".$_POST["chkuser"][$i]."' ";
	$result = mysql_query($sql);			
	$record = mysql_fetch_array($result);
	
	for($n = 1;$n <= 10;$n++){
		if($record["job$n"] != ''){
		}else return $m;
	}
}

	for($i=0;$i<count($_POST["chkuser"]);$i++)
	{
		if($_POST["chkuser"][$i] != "")
		{	
			$sql = " select * from tb_member where username = '".$_POST["chkuser"][$i]."' ";
			$result = mysql_query($sql);			
			$record = mysql_fetch_array($result);
			
			check_job($m);
			$strSQL = " update tb_member set job$m = '$key_job' ";
			$strSQL .=" WHERE username = '".$_POST["chkuser"][$i]."' ";
			$objQuery = mysql_query($strSQL);
		}
	}
mysql_close();
?>