Filtering posts by taxonomy and meta_value

I have finally been able to come up with a solution based on some help from my more MySQL oriented question at Stack Overflow:

add_filter( 'posts_fields', 'posts_fields' );

function posts_fields( $fields ) {
    if ( ( is_woocommerce() || is_search() ) && ! is_admin() ) {
        $add = "
            , CASE wt.slug 
            WHEN 'antique' THEN 1 
            WHEN 'reproduction' THEN 2 
            ELSE 0 END 
            as slug_order
        ";
        return $fields . $add;
    }
    return $fields;
}

add_filter( 'posts_join', 'meta_join' );

function meta_join( $join ) {
    if ( ( is_woocommerce() || is_search() ) && ! is_admin() ) {
        global $wpdb;
        $add = '';
        $add = " 
            LEFT JOIN $wpdb->postmeta stock ON ( 
                $wpdb->posts.ID = stock.post_id 
                AND stock.meta_key = '_stock_status' 
            ) 
            LEFT JOIN $wpdb->term_relationships wtr ON ( 
                $wpdb->posts.ID = wtr.object_id 
                AND stock.meta_value = 'outofstock'
            )
            LEFT JOIN $wpdb->term_taxonomy wtt ON ( 
                wtr.term_taxonomy_id = wtt.term_taxonomy_id 
                AND wtt.taxonomy = 'product_tag'
            ) 
            LEFT JOIN $wpdb->terms wt ON (
                wtt.term_id = wt.term_id 
                AND wt.slug IN( 'antique','reproduction' ) 
            )
        ";
        return $join . $add;
    }
    return $join;
}

add_filter('posts_where', 'hide_sold_antiques');

function hide_sold_antiques( $where ) {
    if ( ! is_product() && ! is_search() && is_woocommerce() && ! is_admin() ) {
        $add = '';
        if ( ! show_sold_antiques() ) {
            global $wpdb;
            $add = " AND NOT ( 
                stock.meta_value = 'outofstock' 
                AND $wpdb->posts.ID IN (
                    SELECT object_id 
                    FROM $wpdb->term_relationships wtr
                    INNER JOIN $wpdb->term_taxonomy wtt ON ( 
                        wtr.term_taxonomy_id = wtt.term_taxonomy_id 
                        AND wtt.taxonomy = 'product_tag'
                    ) 
                    INNER JOIN $wpdb->terms wt ON ( 
                        wtt.term_id = wt.term_id 
                        AND wt.slug = 'antique'
                    )
                )
            ) ";
        }
        $add .= " AND NOT ( 
            stock.meta_value = 'outofstock' 
            AND (
                CASE wt.slug 
                WHEN 'antique' THEN 1 
                WHEN 'reproduction' THEN 2 
                ELSE 0 END
            ) = 0
        ) ";
        return $where . $add;
    }
    return $where;
}

add_filter( 'posts_groupby', 'product_groupby' );

function product_groupby( $groupby ) {
    if ( ( is_woocommerce() || is_search() ) && ! is_admin() ) {
        return $groupby . ', slug_order';
    } else {
        return $groupby;
    }
}

add_filter( 'posts_orderby', 'product_meta_orderby' );

function product_meta_orderby( $orderby ) {
    if ( ( is_woocommerce() || is_search() ) && ! is_admin() ) {
        global $wpdb;
        return " $wpdb->posts.post_type DESC, stock.meta_value ASC, slug_order DESC, $wpdb->posts.post_date DESC ";
    }
    return $orderby;
}

function show_sold_antiques() {
    $show_sold_antiques = false;
    $showsold_parameter = null;
    if ( isset( $_GET[ 'showsold' ] ) ) {
        $showsold_parameter = $_GET[ 'showsold' ];
        if ( $showsold_parameter === 'true' ) {
            $show_sold_antiques = true;
        }
    }
    return $show_sold_antiques;
}