显示类别下子类别的Php代码

<?php
// 假设类别和子类别数据存储在数据库中
// 这里使用MySQL数据库作为示例

// 连接数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查数据库连接是否成功
if ($conn->connect_error) {
    die("数据库连接失败: " . $conn->connect_error);
}

// 查询类别和子类别数据
$sql = "SELECT * FROM categories";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出类别和子类别
    while($row = $result->fetch_assoc()) {
        echo "类别: " . $row["category_name"] . "<br>";
        
        // 查询该类别下的子类别
        $subCategorySql = "SELECT * FROM subcategories WHERE category_id = " . $row["category_id"];
        $subCategoryResult = $conn->query($subCategorySql);
        
        if ($subCategoryResult->num_rows > 0) {
            // 输出子类别
            while($subCategoryRow = $subCategoryResult->fetch_assoc()) {
                echo "子类别: " . $subCategoryRow["subcategory_name"] . "<br>";
            }
        } else {
            echo "该类别下没有子类别<br>";
        }
        
        echo "<br>";
    }
} else {
    echo "没有类别数据";
}

// 关闭数据库连接
$conn->close();
?>