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($_POST['showbtn'])){
        $conn=mysqli_connect("localhost","root","","crud") or die("connection failed") ;
    $stu_id=$_POST['sid'];
    $sql="select *from student where sid={$stu_id}";
    $result=mysqli_query($conn,$sql) or die("query unsucessfull");
    if(mysqli_num_rows($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>
        <?php 
            $sql1= "select *from studentclass";
            $result1=mysqli_query($conn,$sql1) or die("query unsucessfull");

            if(mysqli_num_rows($result1)>0){
               echo '<select name="sclass">';
                while($row1=mysqli_fetch_assoc($result1)){
                   if ($row['sclass']==$row1['cid']){
                       $select="selected";

                   }else{
                       $select="";

                   }
                  echo  "<option {$select} value='{$row1['cid']}'>{$row1['cname']}</option>";
                }
                  echo  "</select>" ;    
            }
          ?>
        </div>
        <div class="form-group">
            <label>Phone</label>
            <input type="text" name="sphone" value="<?php echo $row['sphone']; ?> " />
        </div>
    <input class="submit" type="submit" value="Update"  />
    </form>
    <?php
        }
    }
}
    ?>
</div>
</div>
</body>
</html>