如何使用php比较mysql查询中的两个日期时间

Question

I want to compare two datetime variable witch one of them is current server time and one of them is stored in mysql database i am running this simple piece of code and it wont work and says it is a syntax error i am wondering what can i do

    <?php include("includes/student_session.php");?>
<?php confirm_logged_in();?>
<?php include("includes/connection.php");?>
<?php 
        date_default_timezone_set("");
        $now_date=date("Y-m-d H:i:s");

    $query1="select exam_id from exam where {$now_date} > start_date";
    $result=mysqli_query($cnn,$query1);
    if($result){

    $row=mysqli_fetch_array($result);
    echo $exam_id. "exists";

    }else
    {echo mysqli_error($cnn);}

?>

Answer 1

$query1="select exam_id from exam where {$now_date} > start_date";
$result=mysqli_query($cnn,@query1);

I think the error is because you are using @ insteal of $. Also your query seems to be wrong. You should compare values with fields change it to

   $query1="select exam_id from exam where start_date > '{$now_date}'";
   $result=mysqli_query($cnn,$query1);