SQL:
SELECT *
 FROM 
`cat_items` AS i JOIN (SELECT 
    si.ID_Item, 
    SUM(si.Qty) AS QtyForSale
 FROM 
`stk_items` AS si JOIN `stk_bins` AS sb ON si.ID_Bin = sb.ID
WHERE (si.WhenRemoved IS NULL) AND (sb.isForSale) AND (sb.isEnabled) AND (sb.WhenVoided IS NULL)
GROUP BY si.ID_Item) AS s ON s.ID_Item=i.ID JOIN `cat_title_x_topic` AS tt ON i.ID_Title=tt.ID_Title
WHERE (ID_Topic=1404)