Query Loop within Query Loop .... Need Optimization help

[cinq]

Ok using similar code, I am trying to show a list of authors, and their respective written articles.

This is the code i am trying to use :

PHP Code:

$authorquery = $DB_site->query("
        SELECT * FROM " . TABLE_PREFIX . "articles_article a
        LEFT JOIN " . TABLE_PREFIX . "user u
        ON a.author=u.username
        ORDER BY a.author asc
        ");

$artbyauthorquery = $DB_site->query("
        SELECT articles_articleid, title, author
        FROM " . TABLE_PREFIX . "articles_article
        ORDER BY publishdate desc
        ");

$author_cache = array();
while ($author = $DB_site->fetch_array($artbyauthorquery))
{
    $author_cache[$author['author']][] = $author;
}

// authors
foreach ($author_cache['author'] AS $author)
{
           $userid = $author["userid"];
        $author = $author["author"];

        // articles by the authors
        foreach ($author_cache[$author] AS $article)
        {
            $arttitle=$article["title"];
            $artid=$article["articles_articleid"];
            eval('$authorartbit .= "' . fetch_template('vbArticles_authorartbit') . '";');
        }
     eval('$authorbit .= "' . fetch_template('vbArticles_authorbit') . '";');
}

    $navbits = construct_navbits(array('' => $vbphrase['vbarticles']));
    eval('$navbar = "' . fetch_template('navbar') . '";');
    eval('print_output("' . fetch_template('vbArticles_authorlist') . '");');
} 


However it gives me an error at the line :

PHP Code:

foreach ($author_cache['author'] AS $author) 


Something to do with the 'author' there I think. I need to put in the value there which is the name of the authors, correct ?

foreach works with strings in the array too, so how come this is not accepted ?
error is "Invalid argument supplied for foreach()".