php mysql查询count

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

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

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

$sql = "SELECT COUNT(*) AS total FROM users";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出数据
    while($row = $result->fetch_assoc()) {
        echo "总用户数: " . $row["total"];
    }
} else {
    echo "0 结果";
}
$conn->close();
?>

<?php
$sql = "SELECT COUNT(*) AS active_users FROM users WHERE status = 'active'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "活跃用户数: " . $row["active_users"];
    }
}
?>

<?php
$sql = "SELECT COUNT(DISTINCT product_id) AS unique_products FROM orders";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "不同产品种类数: " . $row["unique_products"];
    }
}
?>