How to write PHP query for specified category products

How to write PHP query for specified categories of products

In the process of website development, it is often necessary to query and display products according to their classification. The following introduces a method of using PHP to write queries for specified category products, and provides specific code examples.

First, we need to create a product table (products) and a category table (categories) in the database, which are related through foreign keys. The product table includes fields: product ID (id), product name (name), product category ID (category_id), etc. The classification table includes fields: classification ID (id), classification name (name), etc.

Next, we write a PHP function to query the products under the specified category ID. The specific code is as follows:

<?php
//连接数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

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

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

//定义查询指定分类商品的函数
function getProductsByCategory($category_id) {
    global $conn;
    
    $sql = "SELECT * FROM products WHERE category_id = " . $category_id;
    $result = $conn->query($sql);
    
    if ($result->num_rows > 0) {
        //输出数据
        while($row = $result->fetch_assoc()) {
            echo "ID: " . $row["id"]. " - 商品名称: " . $row["name"]. "<br>";
        }
    } else {
        echo "0 个结果";
    }
}

//调用函数查询指定分类ID为1的商品
getProductsByCategory(1);

$conn->close();
?>

In the above code, we first connect to the database, and then define a function named getProductsByCategory to query the products under the specified category ID. The function uses the SQL statement SELECT * FROM products WHERE category_id = $category_id to query, and then outputs the query results through a loop.

Finally, we call the getProductsByCategory function and pass in the category ID 1 as a parameter to query the product information of the category ID 1.

Through the above method, we can easily write a PHP function to query the products under the specified category and display them on the website. At the same time, the code can also be modified and optimized according to specific needs.

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