merge 2 condition array from 2 query in 1

I just an amateur in script coding. I need help from somebody here..
I have a trouble here I was tried to show 2 condition merge from my code, look at here please...

<ul class="nav navbar-nav">
   <?php               
   $main=mysql_query("SELECT * FROM mainmenu WHERE aktif='Y'");
   while($r=mysql_fetch_array($main)){
   $t=$r[''];
   $tm="<a href='$r[link]' class='dropdown-toggle' data-toggle='dropdown' role='button' aria-expanded='false'>$r[nama_menu]<span class='caret'></span></a>";
   $th="<a href='$r[link]'>$r[nama_menu]</a>";
   if ($t!= ""){
   $tombol=$th;
   }else{
   $tombol=$tm;
   } 
   echo "<li class='dropdown'>$tombol
         <ul class='dropdown-menu' role='menu'>";
    	 $sub=mysql_query("SELECT * FROM submenu, mainmenu  
         WHERE submenu.id_main=mainmenu.id_main
         AND submenu.id_main=$r[id_main]");
    	 while($w=mysql_fetch_array($sub)){
   echo " <li><a href='$w[link_sub]'>$w[nama_sub]</a></li>";
    	 }
   echo "</ul></li>";}
   ?>
</ul>

I have split it to, to try show them in any condition, and this more relevant, but I can't to merge it, I don't know what I have ti do, look at this please

This is the first condition -->

<ul class="nav navbar-nav">
<?php               
    $main=mysql_query("SELECT  DISTINCT    a.* FROM mainmenu a
    INNER JOIN submenu b ON a.id_main = b.id_main AND a.aktif = 'Y'");
    while($r=mysql_fetch_array($main)){
    echo "<li class='dropdown'><a href='$r[link]' class='dropdown-toggle' data-toggle='dropdown' role='button' aria-expanded='false'>$r[nama_menu]<span class='caret'></span></a><ul class='dropdown-menu' role='menu'>";
    $sub=mysql_query("SELECT * FROM submenu, mainmenu  
    WHERE submenu.id_main=mainmenu.id_main 
    AND submenu.id_main=$r[id_main]");
    while($w=mysql_fetch_array($sub)){
    echo " <li><a href='$w[link_sub]'>$w[nama_sub]</a></li>";
    }
   echo "</ul></li>";} 
?>
</ul>

And Thise the second condition -->

<ul class="nav navbar-nav">
<?php      
  $menu=mysql_query("SELECT  DISTINCT    a.* FROM mainmenu a
  LEFT OUTER JOIN submenu b ON a.id_main = b.id_main WHERE b.id_main is null AND a.aktif = 'Y'");
  while($s=mysql_fetch_array($menu)){
  echo "<li class='dropdown'><a href='$s[link]'>$s[nama_menu]</a></li>";} ?>
</ul>

What I want when merge the INNER JOIN with the LEFT OUTER JOIN is :

if (bla, bla, bla){
echo "Show INNER JOIN";
}else{
echo "Show LEFT OUTER JOIN";
}