PHP MySQL选择脚本

我正在开发一个需要从MySQL数据库中选择数据的应用程序。我目前正在通过浏览器测试PHP脚本，以确保它返回正确的数据。目前的问题是它返回异常"数据库错误！"。我已经包含了我的PHP脚本。

get_agencies_by_city.php

<?php
/*
* Following code will get all agencies matching the query
* Returns essential details
* An agency is identified by agency id
*/
require("DB_Link.php");
$city =  ($_GET['City']);
//query database for matching agency
$query = "SELECT * FROM agency WHERE City = $city";
//Execute query
try {
    $stmt   = $db->prepare($query);
    $result = $stmt->execute();
}
catch (PDOException $ex)    {
    $response["success"] = 0;
    $response["message"] = "Database Error!";
    die(json_encode($response));
}
//Retrieve all found rows and add to array
$rows = $stmt->FETCHALL();

if($rows)   {
    $response["success"] = 1;
    $response["message"] = "Results Available!";
    $response["agencys"] = array();
    foreach ($rows as $row) {
        $agency         = array();
        $agency["AgencyID"] = $row["AgencyID"];
        $agency["AgencyName"]   = $row["AgencyName"];
        $agency["Address1"] = $row["Address1"];
        $agency["City"]     = $row["City"];
        $agency["State"]    = $row["State"];
        $agency["Zip"]      = $row["Zip"];
        $agency["Lat"]      = $row["Lat"];
        $agency["Lon"]      = $row["Lon"];
        //update response JSON data
        array_push($response["agencys"], $agency);
    }
    //Echo JSON response
    echo json_encode($response);
} else  {
    $response["success"] = 0;
    $response["message"] = "No Agency found!";
    die(json_encode($response));
}
?>

这是DB_Link.php

<?php 
// These variables define the connection information the MySQL database 
// set connection...

$options = array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8'); 

try 
{ 
        $db = new PDO("mysql:host={$host};dbname={$dbname};charset=utf8", $username, $password, $options); 
} 
catch(PDOException $ex) 
{ 
        die("Failed to connect to the database: " . $ex->getMessage()); 
} 

$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 

$db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC); 

if(function_exists('get_magic_quotes_gpc') && get_magic_quotes_gpc()) 
{ 
        function undo_magic_quotes_gpc(&$array) 
        { 
            foreach($array as &$value) 
            { 
                if(is_array($value)) 
                { 
                    undo_magic_quotes_gpc($value); 
                } 
                else 
                { 
                    $value = stripslashes($value); 
                } 
            } 
        } 
        undo_magic_quotes_gpc($_POST); 
        undo_magic_quotes_gpc($_GET); 
        undo_magic_quotes_gpc($_COOKIE); 
} 

header('Content-Type: text/html; charset=utf-8'); 

session_start(); 

?>