AES加密不能在php中工作

below code runs in PHP it will returns empty string. But same query run in mysql it shows some values.

<?php
   $encrypt_query = "select aes_encrypt('$string','$key') as encrypt_data";
   $encrypt_result = mysql_query($encrypt_query); 
   print_r($encrypt_result);// it returns resource id #7
   $row = mysql_fetch_array($encrypt_result);
   return $row['encrypt_data'];//it return empty
?>

Try

<?php
   $encrypt_query = "select aes_encrypt('$string','$key') as encrypt_data";
   $encrypt_result = mysql_query($encrypt_query); 
   print_r($encrypt_result);// it returns resource id #7
   while($row = mysql_fetch_array($encrypt_result)){
     echo  $row['encrypt_data'];
   }
?>

//Or

$row = mysql_fetch_row($encrypt_result);
echo $row[0];