为什么＆＃39;数量＆＃39;价值没有显示任何价值？

Question

我试图从数据库表中显示数量值，但它没有在浏览器中显示$quantity值。为什么呢？

<?php

include('connection.php');

# cartexe.php will perform all actions on cart.php

// add Item to Cart
if(isset($_POST['addItemToCart']))
{
    // initialize index.php variables
    $productName = $_POST['productName'];
    $price = $_POST['price'];
    $description = $_POST['description'];
    $quantity = 0;

    // check the cart table to see if the product has been previously added
    $smtp = $conn->prepare('SELECT * FROM cart WHERE Product_Name = :product'); // prepare a statement to fetch the quanity for a particular pprodut... the statement is not executed but merely prepared to do so. 
    $smtp->bindParam(':product', $productName, PDO::PARAM_STR); //bind the productNAme with whatever data supplied hence the statement after : above will be replaced with the actually data.. In additional the statement is set as string hence PDO::PRAM_STR
    $smtp->execute();//finally run the statment

    //var_dump($smtp);
    //find the number of rows affected
    $result = $smtp->fetch(PDO::FETCH_NUM);
    // var_dump($smtp);


    //the data does existed
    if($result > 0)
    {
        $row = $smtp->fetch(PDO::FETCH_ASSOC);
        echo " DATA FOUND";
        echo $row['Quantity'];

        //$quantity++; // increment the quanity if data found
     }
     //no match found
     else
     {
         echo ' No data found';
     }

 }

 ?>

Answer 1

您似乎不需要先尝试尝试

$smtp = $conn->prepare('SELECT * FROM cart WHERE Product_Name = :product'); // prepare a statement to fetch the quanity for a particular pprodut... the statement is not executed but merely prepared to do so. 
    $smtp->bindParam(':product', $productName, PDO::PARAM_STR); //bind the productNAme with whatever data supplied hence the statement after : above will be replaced with the actually data.. In additional the statement is set as string hence PDO::PRAM_STR
   ;//finally run the statment



    //the data does existed
    if( $smtp->execute() )
    {
        $row = $smtp->fetch(PDO::FETCH_ASSOC);
        echo " DATA FOUND";
        echo $row['Quantity'];

        //$quantity++; // increment the quanity if data found
     }

Answer 2

看起来像PDO不会让你获取两次，它只是第一次返回结果，然后它只返回false

$result = $smtp->fetch(PDO::FETCH_ASSOC); // returns result
$result = $smtp->fetch(PDO::FETCH_ASSOC); // returns false

所以，一个解决方案就是

$result = $smtp->fetch(PDO::FETCH_ASSOC);
if($result != false){
//....