-1

产品表结构如下

    CREATE TABLE `products` (
  `id` int(6) unsigned NOT NULL AUTO_INCREMENT,
  `category_id` int(6) unsigned NOT NULL,
  `name` varchar(30) NOT NULL,
  `unit_id` int(6) unsigned NOT NULL,
  `brand_id` int(6) unsigned NOT NULL,
  `orignalCost` int(30) NOT NULL,
  `saleprice` int(30) NOT NULL,
  `deleted` tinyint(1) NOT NULL DEFAULT 0,
  PRIMARY KEY (`id`),
  KEY `fk-to-uom` (`unit_id`),
  KEY `fk-to-brand` (`brand_id`),
  KEY `category_id` (`category_id`),
  CONSTRAINT `fk-to-brand` FOREIGN KEY (`brand_id`) REFERENCES `brands` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `products_ibfk_1` FOREIGN KEY (`category_id`) REFERENCES `categories` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=230 DEFAULT CHARSET=utf8mb4

有人可以告诉我我犯了什么错误，因为 var_dump() 显示 NUll 值......mysqli_fetch_array 有什么错误吗？它显示为“array(1) { [0]=> NULL }”

$selected_items_values = $_POST['product_id']; 
   $prices = [];
   foreach($selected_items_values as $prud)
   {
     if(isset($prud))
     {
      $priceSql = "SELECT saleprice from products where id = ' $prud ' ";
      $price=mysqli_query($db,$priceSql);
      $price = mysqli_fetch_array($price);
      array_push($prices , $price);
      var_dump($prices);

     } 
  }
4

2 回答 2

-1

编辑的答案

这是我创建的示例表。（我删除了外键）

CREATE TABLE `products` (
 `id` int(6) unsigned NOT NULL AUTO_INCREMENT,
 `category_id` int(6) unsigned NOT NULL,
 `name` varchar(30) COLLATE utf8_turkish_ci NOT NULL,
 `unit_id` int(6) unsigned NOT NULL,
 `brand_id` int(6) unsigned NOT NULL,
 `orignalCost` int(30) NOT NULL,
 `saleprice` int(30) NOT NULL,
 `deleted` tinyint(1) NOT NULL DEFAULT 0,
 PRIMARY KEY (`id`)
)

这是示例插入语句

INSERT INTO `products`VALUES (NULL, '1', 'name1', '1', '1', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '2', 'name2', '2', '2', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '3', 'name3', '3', '3', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '4', 'name4', '4', '4', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '5', 'name5', '5', '5', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '6', 'name6', '6', '6', '100', '200', '0');

这是我输入的示例数据。

+----+-------------+-------+---------+----------+-------------+-----------+---------+
| id | category_id |  name | unit_id | brand_id | orignalCost | saleprice | deleted |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  1 |      1      | name1 |    1    |     1    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  2 |      2      | name2 |    2    |     2    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  3 |      3      | name3 |    3    |     3    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  4 |      4      | name4 |    4    |     4    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  5 |      5      | name5 |    5    |     5    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  6 |      6      | name6 |    6    |     6    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+

这是 db connect 通过 PHP 获取所有数据。

$conn = mysqli_connect("$db_host","$db_username","$db_pass","$db_name");
$query = $conn->query("SELECT * FROM `products`;");
var_dump($query);

这是上面的结果。你可以看到我有 6 行。

mysqli_result Object
(
    [current_field] => 0
    [field_count] => 8
    [lengths] => 
    [num_rows] => 6
    [type] => 0
)

为了循环通过 php 对象使用 foreach

foreach ($query as $key => $value) {
  var_dump($value);
}

Foreach 结果就像

Array
(
    [id] => 1
    [category_id] => 1
    [name] => name1
    [unit_id] => 1
    [brand_id] => 1
    [orignalCost] => 100
    [saleprice] => 200
    [deleted] => 0
)

Array
(
    [id] => 2
    [category_id] => 2
    [name] => name2
    [unit_id] => 2
    [brand_id] => 2
    [orignalCost] => 100
    [saleprice] => 200
    [deleted] => 0
)

It continues like that...

为了得到只saleprice使用它，如下所示。

foreach ($query as $key => $value) {
  var_dump($value['saleprice']);
}

所以这是你可以得到的。其余的由你决定，无论你想用它做什么。

于 2021-08-24T08:38:21.270 回答
-1

除了特定于您的实现的错误之外，此代码还有两个重要问题：

  • 您正在循环运行查询，将您正在执行的查询数量相乘并创建额外的数据库流量。
  • 您将不受信任的数据连接到您的查询中，让您自己对 SQL 注入开放

第一个问题的答案是使用SELECT...WHERE...IN...，从而在一个查询中选择所有需要的数据。第二个问题是通过使用准备好的语句来解决的。对于可变长度数据，它们的设置可能很繁琐，但改进的安全性和性能是值得的。

对于您的示例，我们需要查询表单

SELECT `saleprice` FROM `products` WHERE `id` IN (?,?,?);  // could be any number of placeholders here.

    $mysqli = new mysqli('localhost','user','password','schema');
    // create the placeholders
    $paramList = str_repeat("?,", count($_POST['product_id']));
    $query = "select saleprice from products where id in (".trim($paramList, ',').")";
    $stmt = $mysqli->prepare($query);
    // create a string of parameter types
    $types = str_repeat('s', count($_POST['product_id']));  // All $_POST values are strings.
    // Now bind the data to the query
    $stmt->bind_param($types, ...$_POST['product_id']); // Use the ... spread operator to unpack the array
    $stmt->execute();
    $stmt->bind_result($resultData);
    while ($row = $stmt->fetch()) {
        echo $resultData;
        echo "<br>\n";
    }

学分：取自此博客的代码

于 2021-08-24T10:55:10.913 回答