php에서 sql 수정시 문자열 합치기가 잘 안되네요ㅠㅠ 채택완료

</p><p><?
ini_set("display_errors",0);
@header('Content-Type: text/html; charset=euc-kr');
include_once $_SERVER['DOCUMENT_ROOT']."/lib/db.php";
$seq = $_POST['seq'];
$Act = $_POST['Act'];
$project_name = $_POST['project_name'];
$target_cnt = $_POST['target_cnt'];
$reg_date = $_POST['reg_date'];
$sql = "select seq from tbl_project where project_name='".$project_name."'";
$row = mysql_fetch_array(mysql_query($sql));
if($row['seq']){
  
  ?>
  <script type="text/javascript">
  alert('동일한 제품정보가 있습니다!');
  location.href="main_sub003_project_list.php";
  </script>
  <?
  exit;</p><p>}
switch($Act){
  case 'write':
   $sql= "insert into tbl_project(project_name,target_cnt,reg_date) values('".$project_name."',".$target_cnt.",now())";
   $retVal = mysql_query($sql);
   break;
  case 'modify':
   $project_name=$reg_date."".$project_name;
   $sql = "update tbl_project set project_name='".$project_name."',target_cnt=".$target_cnt." where seq=".$seq;
   $retVal = mysql_query($sql);
   break;
}</p><p>if($retVal){
?>
<script type="text/javascript">
alert('처리 완료!');
location.href="main_sub003_project_list.php";
</script>
<?
}else{
?>
<script type="text/javascript">
alert('처리 실패!!');
location.href="main_sub003_project_list.php";
</script>
<?}?> </p><p>