继续转到我的php脚本中的数据库错误2

这是我的发货请求.php

<?php
require("config.inc.php");
if (!empty($_POST)) {
if (empty($_POST['name']) || empty($_POST['mobilenumber']) || empty($_POST['address']) || empty($_POST['city'])  || empty($_POST['postcode']) || empty($_POST['state'])) {
    // Create some data that will be the JSON response 
    $response["success"] = 0;
    $response["message"] = "Please Enter the required marked ** field.";
    die(json_encode($response));
}
else if (strlen($_POST['postcode']) < 5 || strlen($_POST['postcode']) >= 6) {
$response["success"] = 0;
    $response["message"] = "Your postcode should be only 5 numbers.";
die(json_encode($response));               
}
$query = "INSERT INTO shipmentrequest ( name, mobilenumber, address, city, postcode, state) VALUES ( :receivername, :receivermobilenumber, :receiveraddress, :receivercity, :receiverpostcode, :receiverstate) ";
//Again, we need to update our tokens with the actual data:
$query_params = array(
    ':name' => $_POST['name'],
    ':mobilenumber' => $_POST['mobilenumber'],
    ':address' => $_POST['address'],
':city' => $_POST['city'],
    ':postcode' => $_POST['postcode'],
':state' => $_POST['state']
);
//time to run our query, and create the user
try {
    $stmt   = $db->prepare($query);
    $result = $stmt->execute($query_params);
}
catch (PDOException $ex) {
    // For testing, you could use a die and message. 
    //die("Failed to run query: " . $ex->getMessage());
    //or just use this use this one:
    $response["success"] = 0;
    $response["message"] = "Database Error2. Please Try Again!";
    die(json_encode($response));
}
//If we have made it this far without dying, we have successfully added
//a new user to our database.  We could do a few things here, such as 
//redirect to the login page.  Instead we are going to echo out some
//json data that will be read by the Android application, which will login
//the user (or redirect to a different activity, I'm not sure yet..)
$response["success"] = 1;
$response["message"] = "Shipping Service Succesfully Requested!";
echo json_encode($response);
//for a php webservice you could do a simple redirect and die.
//header("Location: login.php"); 
//die("Redirecting to login.php");

} else {
?>
<h1>Shipment Request</h1> 
<form action="shipmentrequest.php" method="post">
    Name:<br /> 
    <input type="text" name="name" value="" /> 
    <br /><br />     
    Mobile Number:<br /> 
    <input type="text" name="mobilenumber" value="" /> 
    <br /><br />
    Address:<br /> 
    <input type="text" name="address" value="" /> 
    <br /><br /> 
    City:<br /> 
    <input type="text" name="city" value="" /> 
    <br /><br /> 
    Postcode:<br /> 
    <input type="text" name="postcode" value="" /> 
    <br /><br /> 
    State:<br /> 
    <input type="text" name="state" value="" /> 
    <br /><br /> 
    <input type="submit" value="Request Service" /> 
</form>
<?php
}
?>

我不知道为什么我只用5个数字填写了我的邮政编码文本字段，它只会跳转到特殊处理，即…Database Error2. Please Try Again!有人能告诉我为什么它会进入catch语句吗？