how to combine two different tables data into a single json object

Question

iam making a json object by the following query

    $arr = array();
        $qs=qq("select main_cat_id,main_cat_name,id,name,cat_id,cat_id_main from main,scheme where main_cat_name='xyz' and cat_id_main=main_cat_id");
        while($obj = mysql_fetch_object($qs))
        {
            $arr[] = $obj;
        }
        $total=sizeof($arr);
        $jsn_obj='{"scheme":'.json_encode($arr).',"totalrow":"'.$total.'"}';

 // this is a mock example

Now iam having another query

Query 2:

    $q=qq("select main_cat_id,main_cat_name,id,name,cat_id,cat_id_main from main,scheme where main_cat_name='xyz' and cat_id_main=main_cat_id order by scheme_1_year DESC");
    while($r=mysql_fetch_array($q))
    {
        $cats_id=$r['cat_id'];
        if($cats_id!=0)
        {
         $qw=qq("select cat_name from category where cat_id='$cats_id'");  // Query 3
         $rw=mysql_fetch_array($qw);
         $catm_name=$rw['cat_name'];
        }
    }
// this is a mock example

both are doing the same thing but the later is calculating some cats name as well.This category table cant be merged with the earlier two tables so i have to calculate this cat_name with another query.

Now i want a json object that should be having all the entries of Query 2 and respective Query 3 result. sumthing like this (if explained in simple words): query 2 result[0] plus query 3 result[0],query 2 result[1] plus query 3 result[1]

How can i club these two results together in a json object. Plz guide!!