为什么这个插入查询不起作用？

Question

我想在按下按钮时添加记录。这是我的PHP：

<?php
            $date="";
            $category_value="";
            $item_value="";
            $vendor_value="";
            $unit_value="";
            $price_rate_value="";
            $quantity_value="";
            $vat_value="";
            $freight_value="";
            $other_charges_value="";
            $total_value="";
             if(  !empty($_POST['category']) && !empty($_POST['item_name']) &&!empty($_POST['vendor_name']) && !empty($_POST['Unit']) && !empty($_POST['Price_per_Unit']) && !empty($_POST['Quantity']) &&  !empty($_POST['VAT']) &&  !empty($_POST['Freight_charges'])&&  !empty($_POST['Other_Charges']))
            {
           //$date=$_POST['datepicker'];
            $category_value=$_POST['category'];
            $item_value=$_POST['item_name'];
            $vendor_value=$_POST['vendor_name'];
            $unit_value=$_POST['Unit'];
            $price_rate_value=$_POST['Price_per_Unit'];
            $quantity_value=$_POST['Quantity'];
            $vat_value=$_POST['VAT'];
            $freight_value=$_POST['Freight_charges'];
            $other_charges_value=$_POST['Other_Charges'];
            $total_value=$price_rate_value * $quantity_value;
            $sth = $conn->prepare('INSERT INTO bill (date, category, item, vendor, unit, price_per_unit, quantity, vat, freight_charges, other_charges, total) VALUES (CURRENT_DATE, :category, :item, :vendor, :unit, :rate, :quantity, :vat, :freight, :other, :total)');
            $sth->execute(array(':category'=>$category_value,':item'=>$item_value,':vendor'=>$vendor_value,':unit'=>$unit_value,':rate'=>$price_rate_value,':quantity'=>$quantity_value,':vat'=>$vat_value,':freight'=>$freight_value,':other'=>$other_charges_value,':total'=>$total_value));
              header( "Refresh: 0;" );}
              ?> 

这是我的HTML：

<form method="POST">
            <input type="submit" name="submit" value="Update" style="width:150px;padding:10px;">

以下是连接代码：

 <?php 
         $servername = "localhost";
        $conusername = "root";
        $conpassword = "";
        $dbname = "annapoorna";
        $dsn='mysql:dbname='.$dbname.';host='.$servername;
        $conn = new PDO($dsn, $conusername, $conpassword);
        ?>

单击按钮时，未插入记录。这是为什么？ 我多次检查过，但是徒劳无功。