Send "Button"-ID on Submit - php

Question

I have an PHP page, which contains a form with some different input fields, e. g. day, month, year etc.. The form method is POST, only one non-editable field (The user ID) is sent via GET.
Of course, there is a "Submit"-Button, which triggers the form Action (PHP Script on Server).
The form tags contain a table with empty cells too. Now comes my question:
If the user clicks into one of the table cells, the form should be submitted, but additional to the regular form data the ID of the table cell should be transmitted too (If via POST or GET doesn't matter to me). How can I do that?
//Edit 2:
...
<form method="post" action="<?= DOMAIN?>/.../addUserTimetable.php?uid=<?= $user->getUserID() ?>">
<select id="day" name="day">
...
</select>
...
<input name="yearend" id="yearend" ...>
<button type="submit">...</button>
<table class="bordered">
<tr>
<th>Std.</th>
<th>Montag</th>
<th>Dienstag</th>
<th>Mittwoch</th>
<th>Donnerstag</th>
<th>Freitag</th>
</tr>
<?php
for($i=1; $i<13;$i++) {
echo "<tr>";
echo "<th>".$i. "</th>";
for($j=1;$j<6;$j++) {
echo "<td id='h".$i. "d".$j. "' onclick='???'></td>";
}
echo "</tr>";
}
?>
</table>
</form>
...
The server sided procession is fine, but I haven't got any ideas - even after two hours google - how I could transmit the cell id additionally.

Answer 1

That shouldn't be to hard. Have a look at the following example:
<form>
<input type="text" name="something">
<table>
<tr>
<td><input type="submit" name="cel1">
</tr>
<tr>
<td><input type="submit" name="cel2">
</tr>
<tr>
<td><input type="submit" name="cel13">
</tr>
</table>
<input type="submit" value="save">
</form>
By giving the submit buttons in the table cells a name attribute, that name will also be present as a key on the $_REQUEST. Go ahead and var_dump the $_REQUEST and you'll see you can find out in the backend which button got pushed by checking which key exists.
Note that POST / GET is completely irrelevant here, both will work just the same. And obviously you could apply some css to those buttons to make them transparent and lay them on top of the table cells, so they don't look like buttons, but just "capture" the user's click.
One last side note, are you sure you want to send the userID as a GET parameter? That would be very easy for someone with bad intentions to manipulate. Consider not sending the ID at all, but keeping it in the session on the server.