how to get the value of query string to check in sql statement..?

hi all,..
as i mention in the Subject . i want to get the qurey string value that i appended to url to make a sql statement ...?

$form['request'][]=array(     
    '#value' => l($obj->v_date,'http://localhost/drupal?q=request/price&'.'vid/'.$obj->id),
	'#type' => 'item',
  );
  

 function show_price() {
  $sql = db_query("SELECT v_price FROM requests ");  //here i want to make where id=" query_string_value" ?????
  while ($obj = db_fetch_object($sql))
  {
  $form['request'][] = array(
    '#type' => 'fieldset',
	 '#title' => t('Vacation Prices'),
	'#value' => $obj->v_price,
   
  );
  
  }
  
  return $form;
  }

thanks for advance