select null link
, to_char(o.order_timestamp, 'DY') label
, sum(decode(p.category,'Mens',oi.quantity * i.unit_price)) "Mens"
, sum (decode(p.category,'Womens',oi.quantity * i.unit_price,0)) "Womens"
, sum (decode(p.category,'Accessories',oi.quantity * oi.unit_price,0)) "Accessories"
from apa$nf_products p
, apa$nf_order_items oi
, apa$nf_orders o
where oi.product_id = p.product_id
and o.order_id = oi.order_id
and (oi.quantity * oi.unit_price) <> 1999
group by to_char(o.order_timestamp, 'DY')
, to_char(o.order_timestamp, 'D')
order by to_char(o.order_timestamp, 'D')