Php 无法选择Timestamp=GET的表

我在这里很困惑，我怎么能选择一个表，其中schedule\u date\u time=$\u GET['date\u time']

<?php

require 'core/init.php';

$schedule_id            =  $_GET['id'];
$schedule_date_time     =  $_GET['date_time'];
$session_id             =  $_GET['session'];
$user_id                =  $_GET['user'];
$user_email             =  $_GET['email'];
$user_name              =  $_GET['username'];
$registry_id            =  $_GET['registry'];

$check1 = DB::getInstance()->query("SELECT * FROM chat_schedule WHERE     schedule_date_time = $schedule_date_time");

if ($check1->count()) {

$insert = DB::getInstance()->insert('chat_booked', array(
        'schedule_id'           => $schedule_id,
        'schedule_date_time'    => $schedule_date_time,
        'session_id'            => $session_id,
        'user_id'               => $user_id,
        'user_email'            => $user_email,
        'user_name'             => $user_name, 
        'registry_id'           => $registry_id
    ));
if ($insert = true) {
    echo "Insert was Successful";
}

} else {
echo "No Match Found, INSERT FAILED!";
}

---

将
$schedule\u date\u time
更改为
“$schedule\u date\u time”
如下：

"SELECT * FROM chat_schedule WHERE     schedule_date_time = '$schedule_date_time' "