ISAM calls/second

I have the following two queries: (HP-UX 10.20, OnLine 7.22) select sum(price * quantity) expdate from podetail, pomaster where pomaster.number = podetail.number and expdate between "01/01/97" and "12/31/97" and chgcode = "5065"; select sum(price * quantity) expdate_odate from podetail, pomaster where pomaster.number = podetail.number and expdate between "01/01/97" and "12/31/97" or (expdate is null and odate between "01/01/97" and "12/31/97") and chgcode = "5065"; as you can see the second one is the same as the first except if expdate is null then drive on odate instead. 'set explain on' gives a cost of 302 for the first and, are you ready for this, 2.1 BILLION for the second. Okay, I'll just change the second one around and code a little better next time, live and learn. Here's the real question; When the second one ran it brought the entire system to a halt. So, I think, I'll just go into the handy old onperf tool and see how many ISAM/PDQ calls this is making. It must be around 30K or more. But instead it totally flat lines. My session has less than 2 calls per second and no-one else has any (less then 1 per second for every other user on the system combined!) What is the reason for this? It seems that the system would go into super access mode, not come to a dead stop. Any thoughts? TIA