如何使用PHP编写库存管理系统中的商品出库功能代码

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "inventory";

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("连接数据库失败: " . $conn->connect_error);
}

<?php
$sql = "SELECT id, name, quantity FROM products";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "商品ID: " . $row["id"]. " - 商品名称: " . $row["name"]. " - 商品数量: " . $row["quantity"]. "<br>";
    }
} else {
    echo "没有商品";
}

<?php
$product_id = $_POST['product_id'];
$quantity = $_POST['quantity'];

// 检查商品数量是否足够
$sql = "SELECT quantity FROM products WHERE id = $product_id";
$result = $conn->query($sql);
$row = $result->fetch_assoc();
if ($quantity > $row["quantity"]) {
    echo "商品数量不足";
    exit;
}

// 更新商品数量
$new_quantity = $row["quantity"] - $quantity;
$sql = "UPDATE products SET quantity = $new_quantity WHERE id = $product_id";
$conn->query($sql);

// 生成销售记录
$sql = "INSERT INTO sales (product_id, quantity, date) VALUES ($product_id, $quantity, NOW())";
$conn->query($sql);

echo "商品出库成功";