php - 在 SQL 语句中在 PHP 中添加时间约束？

Question

目前在我的代码中，任何学生都可以留下任何数量的反馈。我想让每个学生在一个学期内只能给出两个反馈。

我想我也必须在 MySQL 中应用某种主键概念？

这是我的参考代码：

<?php
session_start();

if (isset($_SESSION['user_id'])) {
    if (isset($_SESSION['user_id']) && isset($_POST['r1']) && isset($_POST['r2']) && isset($_POST['r3']) && isset($_POST['r4']) && isset($_POST['suggestion']) && isset($_POST['module'])) {
        $module = $_POST['module'];
        $user = $_SESSION['user_id'];
        $r1 = $_POST['r1'];
        $r2 = $_POST['r2'];
        $r3 = $_POST['r3'];
        $r4 = $_POST['r4'];
        $suggestion = $_POST['suggestion'];
        switch ($module) {
        case 1:
            $query_insert = "INSERT INTO `wp_feedback` VALUES ('" . $user . "','wp','" . $r1 . "','" . $r2 . "','" . $r3 . "','" . $r4 . "','" . $suggestion . "')";
            if (isset($_POST['submit'])) {
                if ($query_run = mysql_query($query_insert)) {
                    echo "<script type='text/javascript'>alert('Sucessfull');</script>";
                    header('Location: feedback.php');
                }
                else {
                    echo "not inserted";
                }
            }

            break;

        case 2:
            $query_insert = "INSERT INTO `wp_feedback` VALUES ('" . $user . "','hssn2','" . $r1 . "','" . $r2 . "','" . $r3 . "','" . $r4 . "','" . $suggestion . "')";
            if (isset($_POST['submit'])) {
                if ($query_run = mysql_query($query_insert)) {
                    echo "<script type='text/javascript'>alert('Sucessfull');</script>";
                    header('Location: feedback.php');
                }
                else {
                    echo "not inserted";
                }
            }

            break;

        case 3:
            $query_insert = "INSERT INTO `wp_feedback` VALUES ('" . $user . "','dwds','" . $r1 . "','" . $r2 . "','" . $r3 . "','" . $r4 . "','" . $suggestion . "')";
            if (isset($_POST['submit'])) {
                if ($query_run = mysql_query($query_insert)) {
                    echo "<script type='text/javascript'>alert('Sucessfull');</script>";
                    header('Location: feedback.php');
                }
                else {
                    echo "not inserted";
                }
            }

        case 4:
        case 3:
            $query_insert = "INSERT INTO `wp_feedback` VALUES ('" . $user . "','ped','" . $r1 . "','" . $r2 . "','" . $r3 . "','" . $r4 . "','" . $suggestion . "')";
            if (isset($_POST['submit'])) {
                if ($query_run = mysql_query($query_insert)) {
                    echo "<script type='text/javascript'>alert('Sucessfull');</script>";
                    header('Location: feedback.php');
                }
                else {
                    echo "not inserted";
                }
            }

            break;

        default:
            echo "select something";
            break;
        }
    }
}
else {
    echo "<script type='text/javascript'>alert('You must be login to View the contents');</script>";
}

?>

Answer 1

伪代码：

SELECT * FROM feedback WHERE studentid=123 AND feedback.insertdate BETWEEN startofthissemesetr AND endofthissemester

$reccount = number of records returned by the above query

if ($reccount > 1) {

    echo "sorry, you already submitted 2 feedbacks this semester!";

} else {

    echo "thank you for submitting your feedback!";
    insert feedback into DB

}