Bagaimana untuk melaksanakan penambahan, pemadaman, pengubahsuaian dan semakan rekod rakan sekelas dalam php dan mysql

<?php
if(isset($_GET[&#39;submit&#39;])){
$name = $_GET[&#39;name&#39;];
$id = $_GET[&#39;id&#39;];
$major = $_GET[&#39;major&#39;];
$class = $_GET[&#39;class&#39;];

$mysqli = new mysqli(&#39;localhost&#39;,&#39;root&#39;,&#39;&#39;,&#39;studentdatabase&#39;);
if(mysqli_connect_errno()){
echo mysqli_connect_error();
exit();
}

$insert_sql = "INSERT INTO student (name,id,major,class) VALUES (&#39;$name&#39;,&#39;$id&#39;,&#39;$major&#39;,&#39;$class&#39;)";

if($mysqli->query($insert_sql)){
echo "添加学生成功";
}else{
echo "添加学生失败";
}
}
?>

<form method="get" action="#">
姓名：<input type="text" name="name">
学号：<input type="text" name="id">
专业：<input type="text" name="major">
班级：<input type="text" name="class">
<input type="submit" name="submit" value="添加学生信息">
</form>

<?php
if(isset($_GET[&#39;modify&#39;])){
$id = $_GET[&#39;id&#39;];

$mysqli = new mysqli(&#39;localhost&#39;,&#39;root&#39;,&#39;&#39;,&#39;studentdatabase&#39;);
if(mysqli_connect_errno()){
echo mysqli_connect_error();
exit();
}

$select_sql = "SELECT * FROM student WHERE id = &#39;$id&#39;";

if($result = $mysqli->query($select_sql)){
$row = $result->fetch_assoc();
?>
<form method="get" action="#">
姓名：<input type="text" name="name" value="<?php echo $row[&#39;name&#39;]; ?>">
学号：<input type="text" name="id" value="<?php echo $row[&#39;id&#39;]; ?>" readonly>
专业：<input type="text" name="major" value="<?php echo $row[&#39;major&#39;]; ?>">
班级：<input type="text" name="class" value="<?php echo $row[&#39;class&#39;]; ?>">
<input type="submit" name="update" value="保存">
</form>

<?php
$result->free();
}
}

if(isset($_GET['update'])){
$name = $_GET['name'];
$id = $_GET['id'];
$major = $_GET['major'];
$class = $_GET['class'];

$mysqli = new mysqli('localhost','root','','studentdatabase');
if(mysqli_connect_errno()){
echo mysqli_connect_error();
exit();
}

$update_sql = "UPDATE student SET name='$name',major='$major',class='$class' WHERE id='$id'";

if($mysqli->query($update_sql)){
echo "学生信息修改成功";
}else{
echo "学生信息修改失败";
}
}
?>

<?php
if(isset($_GET[&#39;delete&#39;])){
$id = $_GET[&#39;id&#39;];

$mysqli = new mysqli(&#39;localhost&#39;,&#39;root&#39;,&#39;&#39;,&#39;studentdatabase&#39;);
if(mysqli_connect_errno()){
echo mysqli_connect_error();
exit();
}

$delete_sql = "DELETE FROM student WHERE id = &#39;$id&#39;";

if($mysqli->query($delete_sql)){
echo "学生信息删除成功";
}else{
echo "学生信息删除失败";
}
}
?>

<?php
if(isset($_POST[&#39;search&#39;])){
$keyword = $_POST[&#39;keyword&#39;];

$mysqli = new mysqli(&#39;localhost&#39;,&#39;root&#39;,&#39;&#39;,&#39;studentdatabase&#39;);
if(mysqli_connect_errno()){
echo mysqli_connect_error();
exit();
}

$select_sql = "SELECT * FROM student WHERE name LIKE &#39;%$keyword%&#39;
OR id LIKE &#39;%$keyword%&#39; OR major LIKE &#39;%$keyword%&#39; OR class LIKE &#39;%$keyword%&#39;";

if($result = $mysqli->query($select_sql)){

while($row = $result->fetch_assoc()){
echo "<tr>";
echo "<td>".$row['name']."</td>";
echo "<td>".$row['id']."</td>";
echo "<td>".$row['major']."</td>";
echo "<td>".$row['class']."</td>";
echo "<td><a href=&#39;?modify=1&id=".$row[&#39;id&#39;]."&#39;>修改</a>  <a href=&#39;?delete=1&id=".$row[&#39;id&#39;]."&#39;>删除</a></td>";
echo "</tr>";
}

$result->free();
}
}
?>

<form method="post" action="#">
<input type="text" name="keyword" value="">
<input type="submit" name="search" value="搜索">
</form>