[PHP] 3단 셀렉트, 3단 select box

<?php
      echo $_POST['aa'];
  echo $_POST['bb'];
  echo $_POST['cc'];
 ?>

 <form method="post">

 <select name="aa">
  <option value="년도">년도</option>
  <option value="2016" <?php if ($_POST['aa']=="2016") echo 'selected="selected"';?>>2016</option>
  <option value="2017" <?php if ($_POST['aa']=="2017") echo 'selected="selected"';?>>2017</option>
 </select>

 <select name="bb">
  <option value="월">월</option>
  <option value="1" <?php if ($_POST['bb']=="1") echo 'selected="selected"';?>>1</option>
  <option value="2" <?php if ($_POST['bb']=="2") echo 'selected="selected"';?>>2</option>
  <option value="3" <?php if ($_POST['bb']=="3") echo 'selected="selected"';?>>3</option>
 </select>

 <select name="cc">
  <option value="일">일</option>
  <option value="01" <?php if ($_POST['cc']=="01") echo 'selected="selected"';?>>01</option>
  <option value="02" <?php if ($_POST['cc']=="02") echo 'selected="selected"';?>>02</option>
  <option value="03" <?php if ($_POST['cc']=="03") echo 'selected="selected"';?>>03</option>
 </select>

 <input type='submit' value='조회'/>

</form>




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