update.php

<?php include 'header.php'; ?>
<div id="main-content">
    <h2>Edit Record</h2>
    <form class="post-form" action="<?php $_SERVER['PHP_SELF'] ?>" method="post">
        <div class="form-group">
            <label>Id</label>
            <input type="text" name="sid" />
        </div>
        <input class="submit" type="submit" name="showbtn" value="Show" />
    </form>

    <?php
    if (isset($_SERVER['showbtn'])) {
        $student_id = $_POST['sid'];
        $student_name = $_POST['sname'];
        $student_address = $_POST['saddress'];
        $student_class = $_POST['sclass'];
        $student_phone = $_POST['sphone'];

        $connection = mysqli_connect("localhost", "root", "", "crud") or die("Couldn't connect'");
        $query = "SELECT * FROM student WHERE sid={$student_id}";
        $result = mysqli_query($connection, $query) or die("Data Send Failed");

        if (mysqli_num_rows($result) > 0) {
            while ($row = mysqli_fetch_assoc($result)) {

    ?>
                <form class="post-form" action="updatedata.php" method="post">
                    <div class="form-group">
                        <label for="">Name</label>
                        <input type="hidden" name="sid" value="<?php echo $row['sid'] ?>" />
                        <input type="text" name="sname" value="<?php echo $row['sname'] ?>" />
                    </div>
                    <div class="form-group">
                        <label>Address</label>
                        <input type="text" name="saddress" value="<?php echo $row['saddress'] ?>" />
                    </div>
                    <div class="form-group">
                        <label>Class</label>
                        <select name="sclass">
                            <option value="" selected disabled>Select Class</option>
                            <option value="1">BCA</option>
                            <option value="2">BSC</option>
                            <option value="3">B.TECH</option>
                        </select>
                    </div>
                    <div class="form-group">
                        <label>Phone</label>
                        <input type="text" name="sphone" value="<?php echo $row['sname'] ?>" />
                    </div>
                    <input class="submit" type="submit" value="Update" />
                </form>
    <?php
            }
        }
    }
    ?>
</div>
</div>
</body>

</html>