How to update mysql data when using explode - php

Question

I have this code to load the month of the birthday that corresponds to the id number:
<?php
$query = "SELECT DISTINCT BIRTHDAY FROM student WHERE IDNO='".$_GET['id']."'";
if($result = mysql_query($query))
{
if($success = mysql_num_rows($result) > 0)
{
?>
<select title="- Select Month -" name="mm" id="mm" class="" >
<?php
while ($row = mysql_fetch_array($result))
list($year,$month,$day)=explode("-", $row['BIRTHDAY']);
?>
<option value="<?php echo $month;?>"><?php echo $month; ?></option>\n";
And this is the form action:
$birthday = mysql_real_escape_string($_POST['mm']);
mysql_query("UPDATE student SET YEAR = FIRSTNAME='$fname', BIRTHDAY='$birthday'
WHERE IDNO ='$idnum'");
What should I do, when I click on the update button, it executes, but I see the undefined offset error is stored in the mysql database and not the month.
I'm just a beginner, can you give me some tips on how can I achieve updating the data

Answer 1

In cases like this... you will have to use 3 selects and then join them to update the database... so, in the form you have something like this:
<select name='month'>
<option value='1'>January</option>
<option value='xx'>etc</option>
</select>
<select name='day'>
<option value='1'>1</option>
<option value='xx'>etc</option>
</select>
<select name='year'>
<option value='1980'>1980</option>
<option value='xx'>etc</option>
</select>
Then... the PHP that receives that data should do something like:
$year = mysql_real_escape_string($_REQUEST['year']);
$month = mysql_real_escape_string($_REQUEST['month']);
$day = mysql_real_escape_string($_REQUEST['day']);
$birthday = $year.'-'.$month.'-'.$day;
mysql_query("UPDATE student SET YEAR = FIRSTNAME='$fname', BIRTHDAY='$birthday'
WHERE IDNO ='$idnum'");
Of course... you have to verify first whether all variables are set or not. You can do so by using the isset method.

Answer 2

Check your update query, It may be wrong in that.
mysql_query("UPDATE student SET YEAR = FIRSTNAME='$fname', BIRTHDAY='$birthday'
WHERE IDNO ='$idnum'");
See this year and firstname, in this year is assigned to null character for you.
Just assign like this,
$birthday = mysql_real_escape_string($_POST['mm']);