This is a  script of a form:
Mssql tables create by the sentence:
create table LU_CO_VIP_CLASS(
      id int IDENTITY (1, 1) NOT NULL,
      vip_class int null,
      class_sum_max varchar(32) null,
      class_sum_min varchar(32) null,
      class_rebate int null
      )
Php program:
<?
$class=$HTTP_POST_VARS['class'];
$rebate=$HTTP_POST_VARS['rebate'];
$costmin=$HTTP_POST_VARS['costmin'];
$costmax=$HTTP_POST_VARS['costmax'];
$id=mssql_connect("localhost","sa","admin") or die("CAN NOT CONNECT");
$db=mssql_select_db("netpass_bak",$id);
if (!empty($class) and !empty($rebate) and !empty($costmin) and !empty($costmax))
{
	$query="if exists (select * from LU_CO_VIP_CLASS
	           where vip_class=$class)
	          begin
	           update LU_CO_VIP_CLASS
	           set class_rebate=$rebate,
	               class_sum_min='$costmin',
	               class_sum_max='$costmax'
	               where vip_class=$class
	          end
	         else 
	           insert into LU_CO_VIP_CLASS (
	                      vip_class,
	                      class_sum_max,
	                      class_sum_min,
	                      class_rebate) 
	                      VALUES (
	                      $class,
	                      $costmax,
	                      $costmin,
	                      $rebate)";            
                  mssql_query($query);
}
$query="select * from LU_CO_VIP_CLASS order by vip_class";
$result=mssql_query($query); //line 78
echo "<font size=5 color=#0000FF><b>CLASS</font></b><br>";
echo "<table width=100% border=1 bordercolor=#FFFFFF cellpadding=1 cellspacing=1><tr bgcolor=#6699FF>";
echo "<td><font size=2>CLASS</font></td>";
echo "<td><font size=2 width=30%>MAX</font></td>";
echo "<td><font size=2>MIN</font></td>";
echo "<td><font size=2>REBATE</font></td></tr>";
while ($arrGuest=mssql_fetch_array($result))
{
      echo "<tr>";
      echo "<td bgcolor=#66CCFF><font size=2>".$arrGuest["vip_class"]."</font></td>";
      echo "<td bgcolor=#66CCFF><font size=2 width=30%>$".$arrGuest["class_sum_max"]."</font></td>";
      echo "<td bgcolor=#66CCFF><font size=2>$".$arrGuest["class_sum_min"]."</font></td>";
      echo "<td bgcolor=#66CCFF><font size=2>".$arrGuest["class_rebate"]."%</font></td>";
      echo "</tr>";
}      
      echo "</table>";
?> 
The error:MS SQL: Query failed in e:\php\vipclass.php on line 78.(database had been modifyed successfully)
But when I cut the segment:"
if exists (select * from LU_CO_VIP_CLASS
	           where vip_class=$class)
	          begin
	           update LU_CO_VIP_CLASS
	           set class_rebate=$rebate,
	               class_sum_min='$costmin',
	               class_sum_max='$costmax'
	               where vip_class=$class
	          end
	         else "
(only inset into) or cut the segment of insert into(only update) ,it's display right.
Is it a bug?