Feteching data from database on multiple checkbox filter in php

I want to fetch data from database on checkbox click,here my code works for single checkbox but it shows " mysql_fetch_assoc() expects parameter 1 to be resource, boolean given in" error on multiple checkbox, Here is my Code,

    if(isset($_POST['submit'])){
if(!empty($_POST['filter'])) {
$valid=true;

$filtering=$_POST['filter'];
       $query_str=" WHERE ";
    foreach ($filtering as $value){
      if ($value=="Arsh Nagar"){
         $query_str .="stylish_name='Arsh nagar'";
      }
      else if ($value=="Padma"){
         $query_str .="stylish_name='Padma'";
      }
      else if ($value=="Kajal Yadav"){
         $query_str .="stylish_name='Kajal Yadav'";
      }
       else if ($value=="Shweta"){
         $query_str .="stylish_name='Shweta'";
      }
       else if ($value=="Harshil"){
         $query_str .="stylish_name='Harshil'";
      }
      $query_str .=" OR ";
    }
    $query_str=substr($query_str,0,-5);
    $sql="SELECT * FROM createdlook ".$query_str;

}
else{
$filter_err="Please Select atleast 1 stylish";
$valid=false;
}
}

 if($valid)
    {

    $result=mysql_query($sql); //here is the error generated
    $images = array();
    $index = 0;

    while($row = mysql_fetch_assoc($result)) // loop to give you the data in an associative array so you can use it however.
    {
         $images[$index] = $row;
         $index++;
    }

I think here is some query problem.please solve it if any error in the query