mysql实现多表查询php

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

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// SQL查询
$sql = "SELECT users.id, users.name, COUNT(orders.id) as order_count
        FROM users
        LEFT JOIN orders ON users.id = orders.user_id
        GROUP BY users.id";

$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出数据
    while($row = $result->fetch_assoc()) {
        echo "id: " . $row["id"]. " - Name: " . $row["name"]. " - Order Count: " . $row["order_count"]. "<br>";
    }
} else {
    echo "0 结果";
}
$conn->close();
?>