U can use a decode statement like

select item,
location,
sum(decode(greatest(d2,d1),d2,order_qty,0) "bet_d2_d1
sum(decode(greatest(d3,d2),d3,order_qty,0) "bet_d3_d2
---


from order;

For performance consideration sign function may be properly
used instead of greatest.

Hope it helps u.