php查询多字段,高手帮帮忙

<?php  2 /* *  3    4 if($_POST["ip"]=="查询"){ $domain=$_POST[domain];  5 $sql="select * from tblhosting where `domain`='$domain' ";   6 $us=mysql_query($sql);   7 $us=mysql_fetch_row($us);      8 if(is_array($us)){  echo "存在！ "; } else echo "不存在！";}  9 ?> 

if($_POST["ip1"]=="查询1"){ $domain1=$_POST[domain1];  if($_POST["ip2"]=="查询2"){ $domain2=$_POST[domain2];  if($_POST["ip3"]=="查询3"){ $domain3=$_POST[domain3];  $where = ' domain1=".$domain1." and domain2=".$domain2." and domain3=".$domain3."';$sql="select * from tblhosting where 1 and  ".$where;