Not get value of select in form - php

Question

I have a proplem with form php. When i submit form it not get value of select option. I try many time and many way but it not work. Help me,please. Thanks
Code:
<form method="post" action="" id="form_search" >
<article class="module width_full">
<header><h3>Thống kê CCU</h3></header>
<div class="module_content">
<fieldset>
<label>Month</label>
<select name="month">
<?php
$stt=0;
$query=mysql_query("select DATE_FORMAT(date,'%m') as month from skycity_log.ccu_log GROUP BY month ORDER BY month ASC") or die (mysql_error());
while($row = mysql_fetch_array($query)){
echo"<option value='$row[month]'>$row[month]</option>";}?>
</select>
</fieldset>
<fieldset>
<label>Year</label>
<select name="year">
<?php
$query=mysql_query("select DATE_FORMAT(date,'%Y') as year from skycity_log.ccu_log GROUP BY year ORDER BY year ASC") or die (mysql_error());
while($row = mysql_fetch_array($query)){
echo"<option value='$row[year]'>$row[year]</option>";}
?>
</select>
</fieldset>
<div class="clear"></div>
</div>
<div class="submit_link">
<input type="submit" name="s_t" value="Search" class="alt_btn">
</div>
</article>
</form>
<?php
if(isset($_POST['s_t'])){
$month=$_POST['month'];
$year=$_POST['year'];
$date = $month."-".$year;
$d=strtotime($date);
echo date("Y-m",$d);
}
?>
Exam: when i choice value = 2 in select 'month' and value = '2015' in select 'year' and submit form then result not = '2015-02' that result ='1970-01'. Why?

Answer 1

You are missing date part in your date parameter.
Try this:
$month=$_POST['month'];
$year=$_POST['year'];
$date = "1-" . $month."-".$year;
$d=strtotime($date);
echo date("Y-m",$d);