ผมจะเช็คค่า จาก check box เพื่อนำมาแสดงครับ

if(value==1) {
  $query1 = mysql_query("SELECT * FROM product WHERE pro_id = 1");
  $result1 = mysql_fetch_array($result1);
} elseif(value==2) {
  $query2 = mysql_query("SELECT * FROM product WHERE pro_id = 2");
  $result2 = mysql_fetch_array($result2);
} elseif(value==3) {
  $query3 = mysql_query("SELECT * FROM product WHERE pro_id = 3");
  $result3 = mysql_fetch_array($result3);
} else {
  $query4 = mysql_query("SELECT * FROM product ");
  $result4 = mysql_fetch_array($result4);
}

<?
   $cdsearch="";
   if($_GET[check1]!='' or $_GET[check2]!='' or $_GET[check3]!=''){
        $cdsearch=" WHERE ";
        $z=0;
        for ($i=1; $i<=3; $i++)  {
            if($_GET["check".$i]!=''){
                if($z!=0){ $cdsearch.=" AND ";}
                $cdsearch.=" pro_id ='".$i."' " ;
                $z++;
            }
        }
   }
   echo $cdsearch;  //เอาไว้ตรวจสอบ code  สมมุติว่าเลือก  1 กับ 3 ก็จะได้  WHERE pro_id ='1'  AND  pro_id ='3'
   $query1 = mysql_query("SELECT * FROM product $cdsearch  ");
   $result1 = mysql_fetch_array($result1);



?>