Use Inner join with ul and li

I think the solution you are trying to find will complicate your project further. Either way it will duplicate unnecessary lines and bring irrelevant data to your query.

Try the most practical and perhaps most agile way for your application that is a WHILE chained, something like this:

<ul>
<?php

    include "../conexao.php";
    $codigo = $_POST['codigo'];
    $nome_cat = $_POST['nome_cat'];
    $nome = $_POST['nome'];

    $query = mysql_query("SELECT codigo, nome_cat FROM categoria ORDER BY nome_cat") or die(mysql_error());

    while($res = mysql_fetch_array($query)) {

        echo '<li><a href="#">'.$res['nome_cat'].'</a>';

        $query2 = mysql_query("SELECT codigo, nome, nome_cat FROM sub_categoria WHERE nome_cat = '".$res['nome_cat']."' ORDER BY nome") or die(mysql_error());
        if(mysql_num_rows($query2) > 0) {
            echo '<ul>';
            while($res2 = mysql_fetch_array($query2)) {
                echo '<li><a href="prod_index_categoria.php?codcategoria='.$res2['codigo'].'">'.$res2['nome'].'</a></li>';
            }
            echo '</ul>';
        }

        echo '</li>';

    }
?>
</ul>

Considerations:

• Always try to list the fields you want in a sql query (as I used them), thus saving database processing to find out which ones are ( * ) to bring you. >

• Use indexes in your tables and not names to reference another table in the database, as well as space, are much faster, see this article .

I hope it helps, hugs

In my view your query is ok, the problem is in the relationship of the tables, once you use the category name for such a relationship. Research and apply the concepts of Foreign key in your tables, which will improve both bank maintenance and performance.

----- Edit

I just realized, what you are asking in the query is not what you want to receive, the correct query would be

SELECT s.codigo, s.nome as sub_categoria, c.nome as categoria FROM sub_categoria s INNER JOIN categoria c ON s.cod_cat = c.cod_cat;