Php 如何正确使用foreach显示mysql表中的数据？

我正在用mysql在php页面上做我学校的时间表，我有一个mysql表，如下所示

klass | day | lesson_name
7A | Monday | lesson1
7A | Monday | lesson5
7A | Monday | lesson3
7A | Tuesday | lesson2
7A | Tuesday | lesson1
7A | Tuesday | lesson4
7A | Wednesday| lesson5
7A | Wednesday| lesson2
7A | Wednesday| lesson1
7A | Thursday | lesson3
7A | Thursday | lesson5
7A | Thursday | lesson4
7А | Friday | lesson2
7А | Friday | lesson3
7А | Friday | lesson5
...And other classes

这是我代码的一部分：

    <table border="1">
      <tr align=center>
        <th>Monday</th>
        <th>Tuesday</th>
        <th>Wednesday</th>
        <th>Thursday</th>
        <th>Friday</th>
      </tr>
      <?php
        //$con = mysqli_connect("localhost", "user", "password", "database");
        //if (mysqli_connect_errno()) {
        //   echo "Failed to connect to MySQL: " . mysqli_connect_error();
        //}
        $klass = $_POST['klass'];
        $res1 = mysqli_query($con, "SELECT * FROM `Timetable` WHERE `klass` LIKE '$klass' AND `day` LIKE 'Monday'");
        $res2 = mysqli_query($con, "SELECT * FROM `Timetable` WHERE `klass` LIKE '$klass' AND `day` LIKE 'Tuesday'");
        $res3 = mysqli_query($con, "SELECT * FROM `Timetable` WHERE `klass` LIKE '$klass' AND `day` LIKE 'Wednesday'");
        $res4 = mysqli_query($con, "SELECT * FROM `Timetable` WHERE `klass` LIKE '$klass' AND `day` LIKE 'Thursday'");
        $res5 = mysqli_query($con, "SELECT * FROM `Timetable` WHERE `klass` LIKE '$klass' AND `day` LIKE 'Friday'");
        foreach ($res5 as $row5) {
            echo "<tr>";
            echo "<td align='center'>$row1[lesson_name]</td>";
            echo "<td align='center'>$row2[lesson_name]</td>";
            echo "<td align='center'>$row3[lesson_name]</td>";
            echo "<td align='center'>$row4[lesson_name]</td>";
            echo "<td align='center'>$row5[lesson_name]</td>";
            echo "</tr>";
        }
      ?>
    </table>

星期一
星期二
星期三
星期四
星期五
对您来说，最好的方法是只进行一次DB查询，一次获取所有课程：

SELECT * FROM `Timetable` WHERE `klass` LIKE '$klass'

然后，您可以根据工作日对值进行分组：

$groupedLessons = array_reduce($allLessons, function($groups, $lesson) {
        if (!array_key_exists($lesson['day'], $groups)) {
            $groups[$lesson['day']] = [];
        }
        $groups[$lesson['day']][] = $lesson;
        return $groups;
    }, []);

现在，您可以使用两个嵌套的foreach循环对数据进行迭代：

foreach($groupedLessons as $day => $lessons) {
    foreach ($lessons as $lesson) {
    ?>
    <tr>
        <td><?= $klass ?></td>
        <td><?= $day ?></td>
        <td><?= $lesson['lesson_name'] ?></td>
    </tr>
    <?php
    }
}

foreach（$groupedLessons作为$day=>$lessons）{
foreach（$lessons作为$lesson）{
?>
如果你
var\u dump（$res5）
你会看到它不是一个数组。我现在会完全忘记PHP，而是专注于MySQL。记住这一点，请参阅：帮助我处理代码，请“此代码不显示任何内容”是一个无用的陈述。解决它并报告具体问题。谷歌这个问题，它已经被回答了很多次。对于初学者，学习如何使用
var_dump（$groupedLessons）
查看您得到了什么。但是，我已经可以告诉您，问题是，
$groupedLessons
不包含课程数组，而是一个mysql资源，您需要循环并将其放入$groupedLessons中。什么是？>和@öцццццццццццццццц109首先编码。这是一种更好的方法（以及
？>
和

foreach($groupedLessons as $day => $lessons) {
    foreach ($lessons as $lesson) {
    ?>
    <tr>
        <td><?= $klass ?></td>
        <td><?= $day ?></td>
        <td><?= $lesson['lesson_name'] ?></td>
    </tr>
    <?php
    }
}