risolto :


$listing_sql = "select " . $select_column_list . " p.products_id,
p.manufacturers_id, p.products_price, p.products_tax_class_id, IF(s.status,
s.specials_new_products_price, NULL) as specials_new_products_price,
IF(s.status, s.specials_new_products_price, p.products_price) as final_price

from (" . TABLE_PRODUCTS ." p
left join " . TABLE_SPECIALS . " s on (p.products_id = s.products_id) ,
" . TABLE_PRODUCTS_DESCRIPTION . " pd, " . TABLE_MANUFACTURERS . " m, " .
TABLE_PRODUCTS_TO_CATEGORIES . " p2c )
left join " . TABLE_CATEGORIES . " c on (p2c.categories_id = c.categories_id)

where
c.categories_status = '1' and p.products_status = '1'
and
p.manufacturers_id = m.manufacturers_id
and
m.manufacturers_id = '" . (int)$_GET['manufacturers_id'] . "'
and
p.products_id = p2c.products_id
and
pd.products_id = p2c.products_id
and
pd.language_id = '" . (int)$languages_id . "'
and
p2c.categories_id = '" . (int)$_GET['filter_id'] . "'";

ora funziona... ma non ho idea del perche' ...... qualcuno conosce qualche video-corso "per principianti" su mysql 5 ?
libri ne ho gia' 3, ma non riesco mai a leggere piu' di un tot di pagine, invece se fossere video, li guarderei mentre ceno.