Vertrekmaand
SELECT GROUP_CONCAT(p.vertrekmaand) AS maanden
FROM shop_products AS p
JOIN shop_pro_cat AS pc ON pc.product_id=p.id
JOIN shop_category AS c2 ON c2.id=pc.cat_id
JOIN shop_category AS c1 ON c1.id=c2.parent_cat_id
WHERE p.tonen<>0 AND p.tonen_overzicht<>0
AND p.vertrekmaand<>''
AND c2.id IN (19
)
AND p.reissoort IN ('Cruises'
)
ORDER BY p.vanafprijs ASC