update immediately inserted rows without updating the older ones - php

Question

if i inserted rows and i want to update one column value of this rows inserted in this immediately process without update this one column value of older rows inserted in previous process
you can see my code and understand more clearly:
<?php
session_start(); ?>
<form action="" method="post" name="data_table">
<tbody >
<?php
require_once("dbconfig.php");
error_reporting(0);
$id=$_POST['id'];
$class=$_POST['class'];
$d = new DateTime('now', new DateTimeZone('Asia/Baghdad'));
$date=$d->format('Y-m-d H:i:s');
$q="select * from students WHERE class='$class'";
$qq=mysql_query($q)
or die(mysql_error());
echo "<table border='2'>
<tr>
<th>الأسم</th>
<th>الحضور</th>
</tr><tr>";
while($row=mysql_fetch_array($qq)){
?>
<input type="hidden" name="class" value="<?php echo $row['class']; ?>" >
<td><input type="checkbox" value="<?php echo $row['id']; ?>" name="id[]" ></td>
<td><b><?php echo $row['username']; ?></td>
<tr>
<?php } ?>
</table>
<?php if (isset($_POST['submit']))
{if(empty($id) || $id==0)
{ echo " please check ";
}
else
{
$impid=implode(", ",$id);
$qdel=mysql_query("INSERT INTO attendees SELECT * FROM `students` WHERE class='$class'");
$qdel=mysql_query("UPDATE attendees set datetime='$date'");
if (isset($qdel)){
echo "<h2> done </h2>";}
}
} ?>
</tbody>
</form>
the problem is the update query updating the value of datetime column in all rows inserted now and before now so my question is how can i make the update query work with each inserting process as separated from previous one
anyone can help please ? thanks

Answer 1

Doing an update right after an insert is inefficient. It also isn't a good idea to rely on the columns of two different tables to always match.
You can insert a static string in your query.
INSERT INTO attendees (column1, column2, column3, datetime)
SELECT column1, column2, column3, '$date' FROM students WHERE class='$class'
However, this breaks a normalization standards of RDBMS. The best way to do this is not duplicate data into attendees, but reference a foreign key to the student ID in attendees. You shouldn't have to update two tables to updates a student's information. I suggest you read up on database normalization before designing a database.