Pues simplemente:
Código PHP:
<?
$sql="select
a.id_contenido,
b.fecha,
b.titulo,
b.resumen,
e.align,
e.descrip,
e.borde,
f.nombre,
group_concat(d.nombre order by d.orden separator ', ')
from gc_portada a
inner join gc_contenidos as b
on b.id_contenido = a.id_contenido
and b.publicada = 1
inner join gc_contenidos_categorias as c
on c.id_contenido = a.id_contenido
inner join gc_categorias as d
on d.id_categoria = c.id_categoria
left join gc_contenidos_imagenes as e
on e.id_contenido = a.id_contenido
and e.orden = 1
left join gc_imagenes as f
on f.id_imagen = e.id_imagen
group by a.id_contenido
order by a.orden";
Un saludo,