This is a small piece of code that can be used when you have multiple submit buttons in the same form in Drupal. By using the “clicked_button” in submit function, we can redirect to a certain page based on the button clicked.

/*
 * Drupal form function
 */
function myform_form() {
    //button 1
    $form['heading'] = array (
        '#type' => 'markup',
        '#value' => t('Welcome to My FORM!!'),
    );
   $form['button_one'] = array (
        '#type' => 'fieldset',
        '#title' => 'BUTTON 1'
    );
    $form['button_one']['desc'] = array (
        '#type' => 'markup',
        '#value' => t('This is button 1 text'),
    );
     $form['button_one']['submit_one'] = array (
        '#value' => t('Button 1'),
        '#type' => 'submit',
    );

    //button 2
    $form['button_two'] = array (
        '#type' => 'fieldset',
        '#title' => 'BUTTON 2'
    );
    $form['button_two']['desc'] = array (
        '#type' => 'markup',
        '#value' => t('This is button 2 text'),
    );
     $form['button_two']['submit_two'] = array (
        '#value' => t('Button 2'),
        '#type' => 'submit',
    );

    return $form;
}

This is the submit function for the form

/*
 * Submit function
 * Use the clicked_button functionality
 */
function myform_form_submit($formID, &$form_state) {
    if($form_state['clicked_button']['#value'] == $form_state['values']['submit_one'])	  //if button 1 is clicked
        $form_state['redirect'] = 'mypath/page_one';	//redirect to whatever page you want
    else if($form_state['clicked_button']['#value'] == $form_state['values']['submit_two'])  //if button 2 is clicked
        $form_state['redirect'] = 'mypath/page_two';
}