mysql 动态sql语句

<?php
$host = 'localhost';
$user = 'root';
$password = 'password';
$dbname = 'testdb';

$conn = new mysqli($host, $user, $password, $dbname);

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

$condition = isset($_GET['condition']) ? $_GET['condition'] : '';

$sql = "SELECT * FROM users";
if (!empty($condition)) {
    $sql .= " WHERE age > $condition";
}

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

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "ID: " . $row["id"]. " - Name: " . $row["name"]. " - Age: " . $row["age"]. "<br>";
    }
} else {
    echo "0 结果";
}
$conn->close();
?>

$stmt = $conn->prepare("SELECT * FROM users WHERE age > ?");
$stmt->bind_param("i", $condition);
$stmt->execute();
$result = $stmt->get_result();

if (!$conn->query($sql)) {
    echo "查询失败: " . $conn->error;
}