PHP mysql选择MAX（）

Question

尝试在MAX()中选择PHP MySQL，但未显示任何结果，也未显示错误（错误显示在

error_reporting(E_ALL);
ini_set('display_errors', 1);

）。

我尝试过：

$user_home = new USER();

$select_max = $user_home->runQuery("SELECT MAX(Gems) AS highest FROM users"); 
$get_max = $select_max->fetch(PDO::FETCH_ASSOC); 
$highest = $get_max['highest'];
echo $highest;

课程文件：

public function __construct()
    {
        $database = new Database();
        $db = $database->dbConnection();
        $this->conn = $db;
    }

    public function runQuery($sql)
    {
        $stmt = $this->conn->prepare($sql);
        return $stmt;
    }

Answer 1

您不执行查询，只是准备它并获取数据...

$select_max = $user_home->runQuery("SELECT MAX(Gems) AS highest FROM users"); 
$select_max->execute();
$get_max = $select_max->fetch(PDO::FETCH_ASSOC); 
$highest = $get_max['highest'];
echo $highest;