select *,gdc_cat_producten.volgnummer as VOLG,gdc_cat_producten.parent as PARENT from gdc_cat_producten,mod_winkelform_btwcodes where proBtw=btwId and gdc_cat_producten.parent=0 and gdc_cat_producten.publiceren=1 group by gdc_cat_producten.volgnummer order by gdc_cat_producten.volgnummer,proId limit 0,20