检查数据库中预订日期的可用性

Question

无论日期是否已获取，我都尝试输出回显脚本。该日期由用户提交。如果日期已过，则应显示无法选择日期的响应。但是，我无法使用php进行检查。我的datetimepicker在jQuery中。

<div class="form-group">
  <label>Select Date</label>
  <input type="text" name="cin" id="datetimepicker" onselect="checkdate();" 
     class="form-control" required autocomplete="off">
  <span id="date_status"></span>
  <input type="button" id="submit-button" value="Submit">
</div>

//我的JAVASCRIPT

    <!--Date time picker-- >
    <script type="text/javascript" >
        $(function () {
            $("#datetimepicker").datepicker({
                dateFormat: "yy/mm/dd",
                minDate: 0
            });
        });
    </script>

    < script >
    function checkedate() {
        var email = document.getElementById("datetimepicker").value;

        if (email) {
            $.ajax({
                type: 'post',
                url: 'checkdata.php',
                data: {
                    email: email,
                },
                success: function (response) {
                    $('#date_status').html(response);
                    if (response == "OK") {
                        return true;
                    }
                    else {
                        return false;
                    }
                }
            });
        }
        else {
            $('#date_status').html("");
            return false;
        }
    }
    < /script>


    //MY PHP CODE

    <? php

include('db.php');

if (isset($_POST['cin'])) {
    $emailId = $_POST['cin'];
    $checkdata = " SELECT cin FROM poolreservation WHERE cin='$emailId' ";
    $query = mysqli_query($con, $checkdata);

    if (mysqli_num_rows($query) > 0) {
        echo "OK";

    }
    else {
        echo "Date address already exists.";
    }
    exit();
}
?>