wordpress plugin for get mysql data

can I know how to Use search method for this php code

   global $wpdb;

   $rows = $wpdb->get_results( "SELECT * FROM table_name WHERE roll_number = value");

   if( !empty($rows) ) {
      $roll_num = $rows->roll_number;
      $full_name = $rows->full_name;
      $percentage = $rows->percentage;
      $result = $rows->result; 
   }



?>

i am very confuse,i want to search data in mysql database using search box,i don't know how to use above code for doing search.

via Chebli Mohamed