I have a form with two select field. The select use onChange="form1.submit()" to submit form. And how I know what select field in the form is selected by user? I have tried to do this with two Submit Button and I can know what button have submitted easily.

```
<?php
if(isset($_POST["select"])) {
        echo "submit";
    }
if(isset($_POST["select2"])) {
        echo "submit2";
    }   

?>
<form id="form1" name="form1" method="post">

<select name="select" id="select" onChange="this.form.submit()">
  <option value="1">Select a</option>
  <option value="1">Select b</option>

</select>
<select name="select2" id="select" onChange="this.form.submit()">
  <option value="2">Select2 a</option>
  <option value="2">Select2 b</option>
</select>
</form>

```